Quick Recipe Version (TL;DR)
Quick Ingredients
- Cooking spray and parchment for three 8-inch round pans
- 1 1/4 cups (160 g) all-purpose flour
- 2 cups (about 200 g) graham cracker crumbs, finely crushed
- 1 3/4 cups (350 g) granulated sugar
- 2 1/2 tsp baking powder + 1/2 tsp baking soda
- 1 1/2 tsp fine sea salt, divided
- 1 tsp ground cinnamon (optional)
- 4 large eggs, room temperature
- 2 cups (455 g) unsalted butter, room temperature, divided
- 1/2 cup (120 ml) neutral oil
- 1 cup (240 ml) whole milk, room temperature
- 1/2 cup (120 ml) sour cream, room temperature
- 4 tsp vanilla extract, divided
- 2 cups (340 g) semisweet or bittersweet chocolate chips or chopped chocolate
- About 2 cups (480 ml) heavy cream, divided
- 4 cups (about 200 g) mini marshmallows + 1–2 cups extra for topping
- 14 oz (400 g) marshmallow creme or fluff
- 4 cups (480 g) powdered sugar, sifted
- Extra graham crackers and graham cracker crumbs for decoration
- 1–2 chocolate bars (for decorating)
Do This
- 1. Prep three 8-inch round pans (grease and line), and preheat oven to 350°F (175°C). Whisk flour, graham crumbs, leaveners, salt, and cinnamon.
- 2. Cream 1/2 cup butter, oil, and sugar; beat in eggs and vanilla. Alternate adding dry ingredients with milk and sour cream. Divide into pans and bake 23–28 minutes. Cool completely.
- 3. Make ganache: pour hot cream over chocolate, rest, then whisk with butter and salt until smooth. Cool until thick and spreadable.
- 4. Broil 4 cups mini marshmallows until deeply golden; stir with melted butter, cream, and salt to make a gooey toasted marshmallow filling.
- 5. Beat 1 1/2 cups butter until creamy; add powdered sugar, salt, vanilla, marshmallow creme, and cream to make fluffy marshmallow buttercream.
- 6. Stack cakes with buttercream “dams,” then fill layers with ganache and toasted marshmallow filling. Chill briefly to firm.
- 7. Frost cake with marshmallow buttercream, add ganache drips (optional), decorate with graham crumbs, chocolate pieces, and mini marshmallows, then gently torch marshmallows on top.
Why You’ll Love This Recipe
- All the flavors of classic campfire s’mores reimagined as a tall, show-stopping birthday cake.
- Moist graham cracker-infused cake layers, rich chocolate ganache, and gooey toasted marshmallow filling in every bite.
- Marshmallow buttercream is fluffy, not-too-sweet, and surprisingly simple for home bakers.
- Perfect for celebrations: it looks bakery-fancy but is totally doable with step-by-step instructions.
Grocery List
- Produce: None
- Dairy: Unsalted butter (about 2 cups / 4 sticks), whole milk, sour cream, heavy cream (about 2 cups), 4 large eggs
- Pantry: Graham crackers, granulated sugar, powdered sugar, all-purpose flour, baking powder, baking soda, fine sea salt, ground cinnamon, vanilla extract, neutral oil, semisweet or bittersweet chocolate (chips or bars), marshmallow creme/fluff, mini marshmallows, cooking spray or extra butter for pans, parchment paper
Full Ingredients
Graham Cracker Cake Layers
- Cooking spray or softened butter, for greasing pans
- Parchment paper circles, for lining three 8-inch (20 cm) round cake pans
- 1 1/4 cups (160 g) all-purpose flour
- 2 cups (about 200 g) graham cracker crumbs, very finely crushed
- 1 3/4 cups (350 g) granulated sugar
- 2 1/2 tsp baking powder
- 1/2 tsp baking soda
- 1 tsp fine sea salt
- 1 tsp ground cinnamon (optional but highly recommended)
- 1/2 cup (115 g) unsalted butter, room temperature
- 1/2 cup (120 ml) neutral oil (such as canola, vegetable, or grapeseed)
- 4 large eggs, room temperature
- 1 cup (240 ml) whole milk, room temperature
- 1/2 cup (120 ml) sour cream, room temperature
- 2 tsp vanilla extract
Chocolate Ganache
- 2 cups (340 g) semisweet or bittersweet chocolate chips or finely chopped chocolate
- 1 1/4 cups (300 ml) heavy cream
- 2 tbsp (28 g) unsalted butter, room temperature
- Pinch fine sea salt
Toasted Marshmallow Filling
- 4 cups (about 200 g) mini marshmallows
- 1 tbsp (14 g) unsalted butter, melted
- 2–3 tbsp (30–45 ml) heavy cream, plus more as needed
- Pinch fine sea salt
Marshmallow Buttercream Frosting
- 1 1/2 cups (340 g) unsalted butter, room temperature
- 4 cups (480 g) powdered sugar, sifted
- 1/2 tsp fine sea salt
- 2 tsp vanilla extract
- 14 oz (400 g) marshmallow creme or marshmallow fluff (about two 7 oz / 200 g jars)
- 2–4 tbsp (30–60 ml) heavy cream, as needed
Decorations
- 1/2 cup (50 g) graham cracker crumbs (for sides and top)
- 4–6 whole graham crackers, broken into large pieces
- 1–2 standard chocolate bars (such as milk chocolate), broken into squares or rectangles
- 1–2 cups (50–100 g) mini marshmallows, for piling on top
- Optional: extra chocolate ganache (thinned with a splash of cream) for drips down the sides
- Optional but ideal: kitchen torch for toasting the marshmallows on top
Step-by-Step Instructions
Step 1: Prep your pans and preheat the oven
Preheat your oven to 350°F (175°C). Make sure your oven rack is in the center position.
Grease three 8-inch (20 cm) round cake pans with cooking spray or softened butter. Line the bottoms with parchment circles, then lightly grease the parchment as well. This helps the delicate graham-infused layers release cleanly.
For best results, bring the eggs, milk, and sour cream to room temperature before you start mixing; this helps the batter come together smoothly and bake evenly.
Step 2: Make the graham cracker cake batter
In a medium bowl, whisk together the all-purpose flour, graham cracker crumbs, baking powder, baking soda, salt, and cinnamon (if using). Set aside.
In a large mixing bowl (or the bowl of a stand mixer fitted with the paddle attachment), beat the room-temperature butter and neutral oil together on medium speed until smooth. Add the granulated sugar and beat on medium-high for 3–4 minutes, until the mixture looks pale and slightly fluffy.
Beat in the eggs one at a time, mixing well after each addition and scraping down the bowl as needed. Add the vanilla extract and mix to combine.
In a separate measuring jug or bowl, whisk together the milk and sour cream until smooth.
On low speed, add the dry ingredients to the butter mixture in 3 additions, alternating with the milk–sour cream mixture in 2 additions (dry, wet, dry, wet, dry). Mix just until the last streaks of flour disappear. Do not overmix; overmixing can make the cake dense.
Step 3: Bake the cake layers and cool completely
Divide the batter evenly among the three prepared pans. If you have a kitchen scale, aim for roughly the same amount of batter in each pan for even layers. Smooth the tops with a spatula.
Bake at 350°F (175°C) for 23–28 minutes, or until the cakes are lightly golden, the centers spring back when gently pressed, and a toothpick inserted in the center comes out with a few moist crumbs but no wet batter.
Let the cakes cool in the pans on a wire rack for 15 minutes. Then run a thin knife around the edges, invert each cake onto the rack, peel off the parchment, and let cool completely, about 1–1 1/2 hours. For easier assembly, you can wrap the cooled layers tightly in plastic and chill or freeze them for about 30 minutes to firm them up.
Step 4: Make the chocolate ganache
Place the chocolate chips or chopped chocolate in a medium heatproof bowl.
In a small saucepan, heat the heavy cream over medium heat until it is steaming and just beginning to simmer around the edges (do not let it boil). Immediately pour the hot cream over the chocolate. Let sit undisturbed for 3–5 minutes to soften the chocolate.
Add the room-temperature butter and a pinch of salt. Starting in the center of the bowl, whisk gently in small circles, gradually working your way outwards, until the mixture is completely smooth and glossy.
Let the ganache cool at room temperature, stirring occasionally, until it thickens to a spreadable consistency, about 30–45 minutes. To speed this up, you can place the bowl in the refrigerator for 5–10 minutes at a time, stirring between chills, but do not let it get too firm or it will be difficult to spread.
Step 5: Make the toasted marshmallow filling
Line a baking sheet with parchment paper and spread 4 cups of mini marshmallows into an even layer. Position an oven rack 6–8 inches (15–20 cm) below the broiler element and preheat your broiler to high.
Broil the marshmallows for 1–3 minutes, until they are puffed, deeply golden, and charred in spots, rotating the pan if needed for even browning. Watch very closely; they can go from perfect to burnt in seconds.
Working quickly, scrape the hot toasted marshmallows into a lightly greased heatproof bowl. Add the melted butter, 2 tbsp of heavy cream, and a pinch of salt. Stir vigorously with a spatula or wooden spoon until the mixture is mostly smooth and cohesive. If it seems too thick or stringy to spread, add more cream 1 teaspoon at a time, stirring well, until it becomes a thick but spreadable, gooey filling.
Let the toasted marshmallow filling cool for about 5–10 minutes. It should still be warm and pliable, but not so hot that it melts the buttercream when layered into the cake.
Step 6: Make the marshmallow buttercream frosting
In a large mixing bowl or stand mixer fitted with the paddle attachment, beat the room-temperature butter on medium-high speed for 3–4 minutes, until very creamy and slightly lighter in color.
Reduce the speed to low and gradually add the sifted powdered sugar, salt, and vanilla extract. Once incorporated, increase the speed to medium-high and beat for 2–3 minutes until fluffy.
Add the marshmallow creme and beat again on medium-high for another 2–3 minutes, until the frosting is thick, smooth, and airy. Add 2 tbsp of heavy cream and beat to combine. If needed, add up to 2 tbsp more cream, a little at a time, until you have a soft, spreadable consistency that will still hold swirls.
Scoop about 1 cup of the buttercream into a piping bag fitted with a large round tip (or into a zip-top bag with a corner snipped off). This will be your “dam” around the layers and some decorative piping at the end. Keep the remaining buttercream covered with plastic wrap pressed directly onto the surface so it does not crust while you assemble the cake.
Step 7: Assemble the cake with ganache and toasted marshmallow layers
If your cake layers domed in the oven, use a long serrated knife to level the tops so they are flat. This helps the cake stack evenly and prevents sliding.
Place a small dollop of buttercream in the center of a cake board or serving plate and set the first cake layer on top, bottom-side down, to anchor it.
Pipe a thick ring (a “dam”) of marshmallow buttercream around the outer edge of the cake layer, about 1/4 inch (6 mm) in from the rim. This ring will hold in the soft fillings.
Spread about one-third of the chocolate ganache inside the buttercream ring in an even layer. Then dollop on about half of the toasted marshmallow filling and gently spread it over the ganache, staying inside the buttercream border.
Set the second cake layer on top and repeat: pipe a buttercream dam, spread another third of the ganache, then the remaining toasted marshmallow filling.
Place the final cake layer on top, upside-down (flat side up) for a perfectly smooth top. Press down gently to secure and check that the cake is level. Refrigerate the assembled cake for 20–30 minutes to firm up the fillings before final frosting.
Step 8: Frost, decorate, and toast the marshmallows
Once the cake is chilled and stable, apply a thin “crumb coat” of marshmallow buttercream over the top and sides of the cake. This first layer will trap any loose crumbs. Chill the cake again for about 20 minutes to set the crumb coat.
Frost the cake with the remaining buttercream, spreading a thicker layer over the top and sides and smoothing with an offset spatula or bench scraper. If you want a ganache drip, thin any remaining ganache with a little warm cream until just pourable, then use a spoon or squeeze bottle to drip it around the upper edge of the cake so it runs slightly down the sides. Let it set for a few minutes.
Press graham cracker crumbs around the lower sides of the cake and sprinkle some over the top for texture. Arrange broken graham cracker pieces and chocolate bar squares decoratively on top. Pile mini marshmallows in the center or around the decorations.
Using a kitchen torch, carefully toast the mini marshmallows on top until they are golden-brown and slightly charred in spots, moving the flame constantly to avoid burning and taking care not to hold the flame too close to the buttercream. If you do not have a torch, place the cake (on a cold sheet pan) under a hot broiler, 8–10 inches (20–25 cm) from the element, for 30–60 seconds, rotating as needed and watching constantly. Chill briefly afterward to re-firm the frosting.
Before serving, let the cake sit at cool room temperature for 30–60 minutes so the ganache and buttercream soften slightly for perfect slices.
Pro Tips
- Use finely ground graham crumbs. Crush graham crackers into a very fine, sand-like texture so they blend smoothly into the batter. Larger pieces can make the layers crumbly.
- Get the ganache just right. For ideal spreading, ganache should be the consistency of soft peanut butter. If it is too runny, chill briefly; if it is too firm, warm it for a few seconds at a time in the microwave and stir.
- Do not skip the buttercream “dam.” The toasted marshmallow filling is gooey by design. The ring of buttercream keeps it neatly contained so your layers stay level and fillings do not ooze out.
- Chill between stages. A short chill after stacking and again after crumb coating makes the cake much easier to frost smoothly and slice cleanly.
- Slice with a warm, sharp knife. For picture-perfect slices that show off the layers, dip a sharp knife in hot water, wipe dry, then cut, wiping the blade between cuts.
Variations
- 2-layer version: Bake the batter in two 9-inch (23 cm) pans instead of three 8-inch pans. Increase the baking time slightly (about 28–32 minutes) and use a bit more filling between the two layers.
- Extra-dark chocolate s’mores cake: Use bittersweet (70%) chocolate for the ganache and add 1–2 tbsp unsweetened cocoa powder to the dry cake ingredients for a deeper, more intense chocolate contrast.
- Peanut butter twist: Swirl 1/3–1/2 cup creamy peanut butter into the cooled ganache before spreading between the layers, and garnish the top with a few roasted peanuts for a peanut butter s’mores vibe.
Storage & Make-Ahead
Once assembled, store the cake covered (a cake dome or large overturned bowl works well) at cool room temperature for up to 1 day, or in the refrigerator for up to 4 days. If refrigerated, let the cake sit at room temperature for about 45–60 minutes before serving so the ganache and buttercream soften.
To make ahead, you can bake the cake layers up to 2 days in advance. Wrap each cooled layer tightly in plastic wrap and store at room temperature, or freeze for up to 2 months (thaw overnight in the refrigerator, still wrapped). The ganache can be made up to 3 days ahead and refrigerated; rewarm gently and stir until spreadable. The marshmallow buttercream is best made the day you assemble, but can be stored airtight in the refrigerator for 1–2 days; bring to cool room temperature and re-whip before using.
Leftover slices can be wrapped and frozen for up to 2 months. Thaw overnight in the refrigerator, then bring to room temperature before enjoying.
Nutrition (per serving)
Approximate values for 1 slice (1/14 of the cake): about 850 calories, 12 g protein, 110 g carbohydrates, 42 g fat, 26 g saturated fat, 3 g fiber, and 95 g sugars. These numbers will vary based on the specific brands and exact amounts used, and on how thickly you apply the frosting and fillings.
