Quick Recipe Version (TL;DR)
Quick Ingredients
- Cake: 1 cup melted unsalted butter, 2 cups sugar, 4 large eggs, 1 1/2 cups all-purpose flour, 1/2 cup unsweetened cocoa powder, 1/2 cup buttermilk, 1 tsp baking powder, 1/4 tsp baking soda, 1/2 tsp salt, 2 tsp vanilla, 1 cup mini marshmallows, 3/4 cup chopped pecans.
- Topping: 2 cups mini marshmallows, 3/4 cup chopped pecans.
- Fudge Frosting: 1/2 cup unsalted butter, 1/3 cup unsweetened cocoa powder, 1/3 cup whole milk, 1/4 tsp salt, 3 cups powdered sugar, 1 1/2 tsp vanilla.
Do This
- 1. Preheat oven to 350°F (175°C). Grease a 9×13-inch metal pan and line with parchment.
- 2. Whisk melted butter and cocoa, then whisk in sugar, eggs, and vanilla. Stir in dry ingredients and buttermilk just until smooth.
- 3. Fold in 1 cup mini marshmallows and 3/4 cup pecans. Spread batter evenly in pan.
- 4. Bake 28–32 minutes, until the center springs back and a toothpick comes out with moist crumbs.
- 5. Immediately sprinkle hot cake with remaining 2 cups marshmallows and 3/4 cup pecans.
- 6. For frosting, simmer butter, cocoa, milk, and salt. Off heat, whisk in powdered sugar and vanilla until smooth and pourable.
- 7. Pour warm frosting over hot cake, letting it soak in around marshmallows and pecans. Cool until just warm, then slice and serve.
Why You’ll Love This Recipe
- Ultra-moist, fudgy chocolate cake that is closer to a brownie than a fluffy sponge.
- Marshmallows and pecans baked inside and piled on top for gooey, crunchy texture in every bite.
- Warm fudge frosting is poured over the cake while hot, so it soaks in and creates a rich, crackly topping.
- Bakes in a simple 9×13-inch pan, perfect for potlucks, holidays, and casual celebrations.
Grocery List
- Produce: Optional: fresh mint or berries for garnish (not traditional, but pretty).
- Dairy: Unsalted butter, eggs, buttermilk, whole milk (or evaporated milk).
- Pantry: Granulated sugar, powdered sugar, all-purpose flour, unsweetened cocoa powder, baking powder, baking soda, fine salt, vanilla extract, mini marshmallows, pecan halves or pieces, nonstick baking spray or butter for the pan.
Full Ingredients
For the Chocolate Cake
- Butter or nonstick baking spray, for greasing the pan
- 1 cup (226 g) unsalted butter, melted and slightly cooled
- 1/2 cup (45 g) unsweetened cocoa powder
- 2 cups (400 g) granulated sugar
- 4 large eggs, at room temperature
- 2 teaspoons pure vanilla extract
- 1 1/2 cups (195 g) all-purpose flour
- 1 teaspoon baking powder
- 1/4 teaspoon baking soda
- 1/2 teaspoon fine sea salt or table salt
- 1/2 cup (120 ml) buttermilk, at room temperature
- 1 cup (50 g) mini marshmallows
- 3/4 cup (85 g) chopped pecans (toasted if you like)
For the Marshmallow-Pecan Topping
- 2 cups (100 g) mini marshmallows
- 3/4 cup (85 g) chopped pecans
For the Warm Fudge Frosting
- 1/2 cup (113 g) unsalted butter
- 1/4 teaspoon fine salt
- 1/3 cup (30 g) unsweetened cocoa powder
- 1/3 cup (80 ml) whole milk or evaporated milk
- 3 cups (360 g) powdered sugar, sifted
- 1 1/2 teaspoons pure vanilla extract
Step-by-Step Instructions
Step 1: Preheat the oven and prepare your pan
Preheat your oven to 350°F (175°C) with a rack in the center. Lightly grease a 9×13-inch metal baking pan with butter or nonstick baking spray. For easy removal and clean cuts, line the bottom with a sheet of parchment paper, leaving a little overhang on two sides, then lightly grease the parchment as well.
If you prefer toasted pecans for extra flavor, spread all of the chopped pecans (both for the batter and topping) on a baking sheet and toast in the preheating oven for 6–8 minutes, stirring once, until fragrant. Let cool before using.
Step 2: Make the chocolate batter base
In a large mixing bowl, whisk together the melted butter and cocoa powder until smooth and glossy. Add the granulated sugar and whisk until fully combined and slightly thickened. Whisk in the eggs one at a time, mixing well after each addition, then whisk in the vanilla.
In a separate medium bowl, whisk together the flour, baking powder, baking soda, and salt. Add about half of the dry ingredients to the butter mixture and stir gently with a spatula or wooden spoon. Pour in all of the buttermilk and stir again, then add the remaining dry ingredients. Mix just until you no longer see dry flour. The batter will be thick and shiny; do not overmix.
Step 3: Fold in marshmallows and pecans
Sprinkle 1 cup mini marshmallows and 3/4 cup chopped pecans over the batter. Use a spatula to gently fold them in so they are evenly distributed throughout. Some marshmallows may sit closer to the top; they will melt into gooey pockets as the cake bakes.
Scrape the batter into the prepared 9×13-inch pan. Spread it into an even layer, smoothing the top and nudging it into the corners. Tap the pan firmly on the counter a few times to release any large air bubbles.
Step 4: Bake until fudgy and set
Transfer the pan to the preheated oven and bake for 28–32 minutes. The cake is done when the edges look set and slightly pull away from the sides of the pan, the top springs back lightly when touched in the center, and a toothpick inserted into the center comes out with moist crumbs (but not wet batter).
Begin checking at 28 minutes; Mississippi Mud Cake is best when a little fudgy rather than dry. While the cake bakes, measure out the marshmallows and pecans for the topping and sift the powdered sugar for the frosting so everything is ready to go.
Step 5: Top the hot cake with marshmallows and pecans
As soon as the cake comes out of the oven, set the pan on a wire rack. Immediately sprinkle the remaining 2 cups mini marshmallows evenly over the hot surface, followed by the remaining 3/4 cup chopped pecans. The heat from the cake will start to soften the marshmallows; that is exactly what you want.
Leave the cake on the rack while you prepare the warm fudge frosting. You want the cake and topping to be hot when the frosting is poured, so it can soak in and create that classic Mississippi mud texture.
Step 6: Cook the warm chocolate fudge frosting
In a medium saucepan, combine the 1/2 cup butter, salt, cocoa powder, and milk. Place over medium heat and cook, whisking constantly, until the butter is melted and the mixture just comes to a gentle simmer around the edges. Do not let it vigorously boil.
Remove the pan from the heat. Gradually whisk in the sifted powdered sugar, about 1/2 cup at a time, whisking until smooth before adding more. When all the sugar is incorporated and the frosting is smooth and glossy, whisk in the vanilla extract. The frosting should be thick but pourable, like warm fudge sauce. If it seems too thick, whisk in 1–2 teaspoons more milk; if too thin, add a spoonful or two of powdered sugar.
Step 7: Pour, set, and serve
While the cake is still hot and the marshmallows are soft, slowly pour the warm fudge frosting over the surface in a back-and-forth motion, trying to cover as much of the top as possible. Use an offset spatula or the back of a spoon to gently nudge the frosting into the corners and over any exposed marshmallows and pecans. Some frosting will sink down around the marshmallows and into the cake, and some will set on top in a shiny layer.
Let the cake cool on a wire rack until the pan is just slightly warm to the touch and the frosting has thickened and set, about 45–60 minutes. For the cleanest slices, you can refrigerate the cooled cake for 20–30 minutes before cutting. Use a sharp knife, wiping it between cuts. Serve squares slightly warm or at room temperature.
Pro Tips
- Use a metal pan. A metal 9×13-inch pan conducts heat better than glass, helping the cake bake evenly and keeping the edges from overbrowning.
- Measure flour lightly. Spoon flour into your measuring cup and level it off instead of scooping straight from the bag, which can pack in too much flour and make the cake dry.
- Sift the powdered sugar. Sifting before whisking into the frosting prevents lumps and gives you that smooth, glossy fudge finish.
- Time the frosting. Start making the frosting during the last 5–10 minutes of baking so it is ready to pour while the cake and marshmallows are still very hot.
- Do not overbake. Pull the cake as soon as a toothpick shows moist crumbs. This keeps the center ultra-moist and fudgy, which is exactly what you want for Mississippi Mud Cake.
Variations
- No-nut version: Omit the pecans entirely if you prefer or need a nut-free dessert. You can replace them with an extra 1/2–1 cup mini marshmallows or 1/2 cup chocolate chips sprinkled in the batter and on top.
- Mocha Mud Cake: Stir 1–2 teaspoons instant espresso powder into the cocoa for the cake batter and another 1 teaspoon into the frosting. This deepens the chocolate flavor without making the cake taste overtly like coffee.
- Bourbon-kissed frosting: After removing the frosting from the heat and whisking in the powdered sugar, stir in 1–2 tablespoons bourbon or dark rum along with the vanilla. This adds a subtle, grown-up warmth that pairs beautifully with the chocolate and pecans.
Storage & Make-Ahead
Let the cake cool completely before covering. Store the pan tightly covered with foil or a lid at room temperature for up to 2 days. Because of the marshmallows and frosting, the cake actually stays very moist and may even taste better on day two.
For longer storage, refrigerate for up to 4–5 days. Bring the cake back to room temperature before serving for the best texture, or briefly warm individual slices in the microwave (about 10–15 seconds) to revive the gooey marshmallow layer.
To freeze, cut the cooled cake into squares, wrap each piece tightly in plastic wrap, then place in an airtight container or freezer bag. Freeze for up to 2 months. Thaw overnight in the refrigerator or at room temperature for 1–2 hours, then serve at room temperature.
For partial make-ahead, you can toast the pecans, measure the dry ingredients, and line the pan a day in advance. Because the magic of this cake comes from pouring the warm frosting over a hot cake, it is best to bake and assemble on the same day you plan to serve it.
Nutrition (per serving)
Approximate values for 1 of 16 servings: about 520 calories; 26 g fat (13 g saturated); 68 g carbohydrates; 53 g sugar; 1.5 g fiber; 7 g protein; 220 mg sodium. These numbers are estimates and will vary depending on the specific brands and exact portion sizes you use.
