Quick Recipe Version (TL;DR)

Yield: 12–14 servings (one 3-layer 8-inch cake)
Prep Time: 1 hour
Cook Time: 35 minutes
Total Time: 3 hours (including cooling and chilling)

Quick Ingredients

Butter or baking spray and cocoa powder, for 3 x 8-inch round pans
2 1/2 cups (325 g) all-purpose flour
3 cups (600 g) granulated sugar
1 cup (90 g) unsweetened cocoa powder
2 1/2 tsp baking powder + 2 tsp baking soda + 1 1/2 tsp fine salt
3 large eggs, room temperature
1 1/2 cups (360 ml) buttermilk, room temperature
3/4 cup (180 ml) neutral oil (canola, vegetable, or grapeseed)
1 1/4 cups (300 ml) hot brewed coffee (or very hot water)
3 tsp pure vanilla extract (2 tsp for cake, 1 tsp for mousse or buttercream)
1 cup (170 g) mini semisweet chocolate chips, plus 1/2 cup (85 g) extra for decorating
Chocolate mousse filling (Option 1): 8 oz (225 g) semisweet chocolate, 2 cups (480 ml) cold heavy cream, 3 tbsp (24 g) powdered sugar, 2 tbsp (10 g) cocoa powder, pinch salt
OR chocolate buttercream filling (Option 2): 1 1/2 cups (340 g) unsalted butter, 4 1/2 cups (540 g) powdered sugar, 1/2 cup (45 g) cocoa powder, 1/4 tsp salt, 1/4 cup (60 ml) heavy cream, 2 tsp vanilla, 4 oz (115 g) melted semisweet chocolate
Ganache frosting: 16 oz (450 g) dark chocolate (60–70%), 2 cups (480 ml) heavy cream, 2 tbsp (28 g) unsalted butter
Optional garnish: extra chocolate chunks/curls, fresh berries, cocoa powder

Do This

1. Preheat oven to 350°F (180°C). Grease and line three 8-inch round cake pans with parchment; dust with cocoa.
2. Whisk flour, sugar, cocoa, baking powder, baking soda, and salt. In another bowl whisk eggs, buttermilk, oil, and vanilla. Stir wet into dry, then slowly mix in hot coffee. Fold in 1 cup chocolate chips.
3. Divide batter between pans and bake 28–32 minutes, until a toothpick comes out with a few moist crumbs. Cool 15 minutes in pans, then fully on racks.
4. Make either the chocolate mousse or chocolate buttercream filling. Chill mousse briefly until spreadable, or keep buttercream at cool room temperature.
5. For ganache, pour hot cream over chopped dark chocolate, rest 5 minutes, then stir smooth. Add butter, cool until thick but spreadable.
6. Level cooled cakes. Layer cake with filling between each layer, sprinkling a few extra chips if you like. Apply a thin crumb coat of ganache; chill 20–30 minutes.
7. Frost top and sides with remaining ganache. Press extra chips or chunks onto sides and top. Chill 30 minutes to set before slicing.

Why You’ll Love This Recipe

Triple chocolate in every bite: deep dark cake, fluffy chocolate filling, and silky ganache frosting.
Three textures: tender crumb, airy mousse or buttercream, and rich, glossy ganache studded with chocolate chips.
Birthday-worthy presentation that looks professional but uses simple, home-cook-friendly techniques.
Flexible filling options: choose lighter chocolate mousse or classic chocolate buttercream.

Grocery List

Produce: Fresh raspberries or strawberries (optional garnish), fresh mint (optional garnish)
Dairy: Buttermilk, heavy cream, unsalted butter, large eggs
Pantry: All-purpose flour, granulated sugar, powdered sugar, unsweetened cocoa powder, baking powder, baking soda, fine salt, neutral oil, vanilla extract, brewed coffee (or instant coffee and water), dark chocolate, semisweet chocolate, chocolate chips or chunks, nonstick spray or extra butter for pans

Full Ingredients

For the Dark Chocolate Cake Layers (three 8-inch rounds)

Butter or baking spray and cocoa powder, for greasing and dusting pans
2 1/2 cups (325 g) all-purpose flour
3 cups (600 g) granulated sugar
1 cup (90 g) unsweetened cocoa powder (natural or Dutch-process)
2 1/2 tsp baking powder
2 tsp baking soda
1 1/2 tsp fine sea salt (or table salt)
3 large eggs, at room temperature
1 1/2 cups (360 ml) buttermilk, at room temperature
3/4 cup (180 ml) neutral oil (canola, vegetable, or grapeseed)
2 tsp pure vanilla extract
1 1/4 cups (300 ml) hot brewed coffee (or very hot water)

For the Chocolate Chips & Garnish

1 cup (170 g) mini semisweet chocolate chips or finely chopped chocolate, for folding into the batter
1 tbsp (8 g) all-purpose flour, for tossing with the chips (helps prevent sinking)
1/2 cup (85 g) additional chocolate chips or chunks, for decorating the outside
Optional: chocolate curls or shavings, for the top
Optional: fresh raspberries or strawberries and a few mint leaves, for serving

For the Chocolate Mousse Filling (Option 1)

8 oz (225 g) semisweet chocolate, finely chopped
2 cups (480 ml) cold heavy cream, divided
3 tbsp (24 g) powdered sugar
2 tbsp (10 g) unsweetened cocoa powder, sifted
1 tsp pure vanilla extract
Pinch of fine salt

For the Chocolate Buttercream Filling (Option 2)

1 1/2 cups (340 g) unsalted butter, very soft but not melted
4 1/2 cups (540 g) powdered sugar, sifted
1/2 cup (45 g) unsweetened cocoa powder, sifted
1/4 tsp fine salt
1/4 cup (60 ml) heavy cream, plus 1–2 tbsp more as needed
2 tsp pure vanilla extract
4 oz (115 g) semisweet chocolate, melted and cooled to room temperature

For the Chocolate Ganache Frosting

16 oz (450 g) dark chocolate (60–70% cocoa), finely chopped
2 cups (480 ml) heavy cream
2 tbsp (28 g) unsalted butter, at room temperature

Step-by-Step Instructions

Step 1: Prep the pans and ingredients

Preheat your oven to 350°F (180°C) with a rack in the center. Lightly grease three 8-inch (20 cm) round cake pans with butter or baking spray. Line the bottoms with parchment paper circles, then grease the parchment and dust the pans lightly with cocoa powder, tapping out any excess. This helps the cakes release cleanly and keeps the edges dark and chocolatey.

Bring the eggs and buttermilk to room temperature if possible (about 30 minutes on the counter). Measure out all remaining ingredients so they are ready to go. Chop the dark chocolate and semisweet chocolate, and set them aside in separate bowls for the mousse/buttercream and ganache.

Step 2: Make the dark chocolate cake batter

In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt until completely combined and no streaks of cocoa remain. This step ensures the leaveners are evenly distributed.

In a separate medium bowl, whisk the eggs, buttermilk, oil, and vanilla until smooth. Pour the wet mixture into the dry ingredients. Using a whisk or a mixer on low speed, mix just until everything is mostly combined; the batter will be quite thick at this point.

Slowly pour in the hot coffee (or hot water) while mixing on low, until the batter is smooth and fairly thin. Scrape down the sides and bottom of the bowl to catch any pockets of dry ingredients. In a small bowl, toss 1 cup (170 g) mini chocolate chips with 1 tbsp (8 g) flour, then gently fold them into the batter. The batter will look pourable and glossy.

Step 3: Bake the cake layers and cool completely

Divide the batter evenly among the three prepared pans. An easy way is to use a scale; each pan should get about one-third of the total batter. Smooth the tops with a spatula so they bake evenly.

Bake for 28–32 minutes, or until the cakes are risen, the tops spring back lightly when touched, and a toothpick inserted into the center comes out with a few moist crumbs but no wet batter.

Allow the cakes to cool in their pans on a wire rack for 15 minutes. Then run a thin knife around the edge of each cake, invert onto the rack, and gently peel off the parchment. Flip the layers right-side up and let them cool completely, at least 45–60 minutes. For the easiest assembly, wrap the cooled layers in plastic wrap and chill them in the refrigerator for at least 30 minutes; cold cake crumbs less.

Step 4: Prepare your chocolate filling (mousse or buttercream)

For chocolate mousse filling (Option 1): Place the chopped semisweet chocolate and 1/2 cup (120 ml) of the cold heavy cream in a heatproof bowl. Gently melt the mixture in the microwave in 20–30 second bursts, stirring between each, until smooth, or melt over a saucepan of barely simmering water (double boiler). Set aside to cool to lukewarm; it should be fluid but not hot.

In a chilled mixing bowl, combine the remaining 1 1/2 cups (360 ml) cold heavy cream, powdered sugar, cocoa powder, vanilla, and a pinch of salt. Whip with a hand mixer or stand mixer on medium-high speed until soft-to-medium peaks form. Gently fold one-third of the whipped cream into the cooled chocolate to lighten it, then fold in the rest just until no streaks remain. Cover and refrigerate for 20–30 minutes, until slightly thickened and spreadable.

For chocolate buttercream filling (Option 2): In a large bowl, beat the softened butter with a mixer on medium-high speed for 2–3 minutes until very light and creamy. Gradually add the powdered sugar, cocoa powder, and salt, mixing on low at first to avoid a sugar cloud, then increasing to medium until combined. Beat in the vanilla and 1/4 cup (60 ml) heavy cream and continue beating for 2–3 minutes until fluffy. Finally, pour in the cooled melted semisweet chocolate and beat just until smooth and silky. If the buttercream is too thick, add extra cream 1 tbsp at a time; if too soft, chill briefly.

Step 5: Make the chocolate ganache frosting

Place the finely chopped dark chocolate in a large heatproof bowl. In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer around the edges and small bubbles appear; do not let it boil. Immediately pour the hot cream over the chocolate, making sure all the chocolate is submerged. Let it sit undisturbed for 5 minutes to soften the chocolate.

After 5 minutes, gently whisk from the center outward until the mixture is smooth and glossy. Add the butter and whisk until fully melted and incorporated. At this point the ganache will be quite fluid. Let it cool at room temperature, stirring occasionally, for 30–45 minutes, until it thickens to a spreadable consistency similar to soft frosting. If it gets too firm, you can briefly warm the bowl over a pan of warm water, stirring constantly, until loosened.

Step 6: Level, fill, and stack the cake

Once the cake layers are completely cool, use a long serrated knife to level any domed tops so the layers are flat and even. Place a small dollop of ganache onto your serving plate or cake board to keep the cake from sliding, then set the first layer down, cut side up.

Spread a generous layer of chocolate mousse or buttercream (about 1/3 to 1/2 of your chosen filling) over the first layer, going right to the edges. If you like extra texture, sprinkle a tablespoon or two of chocolate chips on top of the filling. Place the second cake layer on top, cut side up again, and repeat with another layer of filling and optional chips. Finally, place the third layer on top, cut side down for the smoothest finish.

Using an offset spatula, spread a very thin layer of ganache over the top and sides of the stacked cake to create a crumb coat. This traps any loose crumbs. Chill the cake for 20–30 minutes, until the crumb coat is firm to the touch.

Step 7: Frost with ganache and decorate with chocolate chips

Once the crumb coat is set and the ganache has a soft, spreadable consistency, apply a thicker layer of ganache over the top and sides of the cake. Use an offset spatula or bench scraper to smooth the sides for a clean, tall look, or create rustic swoops and swirls if you prefer a more relaxed style.

While the ganache is still soft, gently press the remaining 1/2 cup (85 g) of chocolate chips or chunks around the bottom edge of the cake, or scatter them generously over the top. You can also add chocolate curls or shavings and a few fresh berries for a birthday-worthy finish.

Chill the finished cake for at least 30 minutes to set the ganache. For the best flavor and texture, let the cake sit at cool room temperature for 20–30 minutes before slicing. Use a sharp, warm knife (run under hot water and wiped dry) for the cleanest slices.

Pro Tips

Use room-temperature ingredients for the batter. Room-temp eggs and buttermilk help the batter mix smoothly and bake up with an even, tender crumb.
Weigh your ingredients if possible. Using a kitchen scale, especially for flour, sugar, and cocoa, gives more consistent results and avoids dry or dense cake.
Chill cakes before frosting. Slightly cold cake layers are much easier to stack and frost without tearing or shedding crumbs.
Choose good-quality chocolate. Use dark chocolate around 60–70% cocoa for the ganache and a milder semisweet for the mousse or buttercream for nice contrast.
Adjust ganache texture as needed. If it is too runny, chill briefly and stir; if too firm, gently warm it over a bowl of warm water while stirring.

Variations

Mocha Triple Chocolate Cake: Use strong coffee or espresso for the hot liquid in the batter and add 1–2 tsp instant espresso powder to the ganache for a deep mocha flavor.
Salted Caramel Triple Chocolate Cake: Drizzle a few tablespoons of salted caramel sauce over each mousse or buttercream layer before stacking, and finish the top of the cake with a light sprinkle of flaky sea salt.
Birthday Sprinkle Twist: Use the chocolate buttercream option and fold a handful of colorful sprinkles into the filling layer for a funfetti-style surprise inside the rich chocolate cake.

Storage & Make-Ahead

If using chocolate mousse filling: Because the mousse is cream-based, store the cake tightly covered in the refrigerator for up to 3 days. For the best flavor, let slices sit at room temperature for 20–30 minutes before serving so the ganache and mousse soften slightly. You can bake the cake layers up to 2 days ahead, wrap them well, and refrigerate or freeze them. Assemble with mousse on the day you plan to serve if you want the filling at its fluffiest.

If using chocolate buttercream filling: The fully assembled cake can be kept covered at cool room temperature for up to 2 days, or refrigerated for up to 5 days. Bring to room temperature before serving. Both buttercream and ganache can be made 1–2 days in advance and refrigerated; let them soften and rewhip (buttercream) or gently warm (ganache) before using.

Freezing: You can freeze unfrosted cake layers, well wrapped, for up to 2 months. Thaw overnight in the refrigerator. Leftover slices of the finished cake also freeze well when wrapped individually; thaw overnight in the fridge, then let sit at room temperature before enjoying.

Nutrition (per serving)

Approximate values for 1 slice (1/12 of the cake) using chocolate mousse filling and ganache: about 700 calories; 10 g protein; 82 g carbohydrates; 4 g fiber; 65 g total sugars; 36 g fat (22 g saturated fat); 220 mg sodium. Using buttercream instead of mousse will be slightly higher in fat and calories. These numbers are estimates and will vary with specific ingredients and portion sizes.

Decadent Triple Chocolate Birthday Cake With Ganache and Mousse