Bumpy Cake (A Detroit Classic)

This is a legendary Michigan dessert, famously from Sanders Candy. It features a rich devil’s food cake topped with distinctive parallel rows of buttercream, all enrobed in a shiny, fudgy chocolate icing that cracks and creates the signature “bumps.”

Ingredients

Cake:

• 1 (15.25 oz) box devil’s food chocolate cake mix

• Ingredients listed on box (typically eggs, oil, water)

Buttercream Ridges:

• 4 tablespoons (½ stick / 57g) unsalted butter, softened

• 1 ½ cups (180g) powdered sugar, sifted

• ½ teaspoon vanilla extract

• 1 tablespoon milk or cream

• Pinch of salt

Fudge Icing:

• ½ cup (120ml) buttermilk

• 2 tablespoons light corn syrup

• ½ cup (1 stick / 113g) unsalted butter

• ⅔ cup (55g) unsweetened cocoa powder, sifted

• 3 ½ cups (420g) powdered sugar, sifted

• Pinch of salt

• ½ teaspoon vanilla extract

Step-by-Step Instructions

Part 1: Bake the Cake

1. Preheat oven and prepare a 9×13-inch metal baking pan by greasing and flouring it, or lining it with parchment paper.

2. Prepare the cake batter exactly as directed on the box.

3. Pour batter into the prepared pan and bake according to package directions (usually 28-35 minutes), or until a toothpick inserted in the center comes out clean.

4. Let the cake cool completely in the pan on a wire rack. The cake must be at room temperature before the next steps.

Part 2: Make & Pipe the Buttercream Ridges

1. In a medium bowl, beat the softened butter until creamy.

2. Gradually add the sifted powdered sugar, milk, vanilla, and salt. Beat on medium-high speed for 2-3 minutes until very smooth, light, and pipeable. It should be thick enough to hold a shape.

3. Transfer buttercream to a piping bag fitted with a large round tip (like Wilton 1A or a ½-inch diameter opening). If you don’t have a bag, use a heavy-duty zip-top bag with a corner snipped off.

4. Pipe 10-12 parallel lines of buttercream lengthwise across the entire cooled cake, spacing them about ¾-inch to 1 inch apart. These are your iconic “bumps.” Ensure they are straight and touch from end to end.

Part 3: Make the Fudge Icing & Glaze the Cake

1. Combine and Melt: In a medium saucepan over medium heat, combine the buttermilk, corn syrup, and butter. Heat until the butter is melted and the mixture just begins to simmer at the edges. Do not boil.

2. Whisk in Cocoa: Remove from heat. Immediately whisk in the sifted cocoa powder and salt until completely smooth.

3. Add Sugar: Gradually whisk in the sifted powdered sugar until the icing is smooth, glossy, and pourable. It should be slightly thinner than frosting but thicker than a glaze. Stir in the vanilla.

4. Ice Immediately: While the icing is still warm and fluid, carefully pour it over the entire cake, starting at one long end and moving back and forth to cover the buttercream ridges completely. Use an offset spatula to gently guide it to the edges and ensure full coverage. The icing will settle into the grooves, creating the bumpy texture.

5. Let Set: Allow the cake to sit at room temperature for at least 1-2 hours for the icing to set into a shiny, fudgy shell.

Pro-Tips for the Perfect Bumpy Cake

• Cool Cake Completely: A warm cake will melt the buttercream and ruin the icing.

• Sift Dry Ingredients: Sifting the powdered sugar and cocoa powder prevents lumps in both the buttercream and icing.

• Icing Consistency is Key: The fudge icing should be warm and fluid enough to pour and self-level, but thick enough to coat and not just run off. If it seems too thick, add a teaspoon of warm buttermilk. If too thin, add a bit more sifted powdered sugar.

• Work Quickly with Warm Icing: It will begin to set as it cools. Pour and spread it immediately after mixing.

• The Signature Look: The magic happens when the icing drapes over the buttercream ridges. Don’t spread it too thin—you want a substantial fudge layer.

• Chill for Clean Slices: For the sharpest slices, chill the set cake in the refrigerator for 30 minutes before cutting with a warm knife.

Storage & Serving

• Store covered at cool room temperature for up to 2 days or in the refrigerator for up to 5 days. The fudge icing will soften at room temperature and firm up when chilled.

• Serve at room temperature for the best texture and fudgy flavor.

Enjoy this decadent, nostalgic treat where every slice delivers the perfect combination of moist cake, sweet buttercream, and rich fudge!