Go Back
+ servings

Bumpy Cake

piece of Bumpy Cake on a plate
This bumpy cake is a vintage cake recipe that is full of rich chocolate decadence and ribbons of vanilla buttercream
Prep Time 45 mins
Cook Time 30 mins
Chill Time 2 hrs 15 mins
Total Time 3 hrs 30 mins
Course Dessert
Cuisine American
Servings 12
Calories 742 kcal


Chocolate Cake

  • 15.25 ounces dark chocolate fudge cake mix (I used Duncan Hines brand)
  • ¾ cup unflavored brewed coffee, cooled to room temperature
  • ¾ cup whole milk
  • ½ cup vegetable oil
  • ½ cup sour cream
  • 1 teaspoon vanilla extract
  • 4 large eggs, room temperature

Buttercream Filling

  • ¾ cup sweet cream butter, room temperature
  • teaspoons vanilla extract
  • ¼ teaspoon salt
  • 3 cups powdered sugar, sifted
  • 4 tablespoons heavy cream

Chocolate Frosting

  • 1 cup light brown sugar, lightly packed
  • ¾ cup unsalted butter, room temperature
  • cup buttermilk
  • ½ cup unsweetened cocoa powder
  • ¼ cup light karo, corn syrup
  • ½ teaspoon salt
  • 3 cups powdered sugar, sifted
  • teaspoons vanilla extract


Chocolate Cake

  • Preheat the oven to 350°F. Spray a 9x13 metal baking dish with baking spray (Baker’s Joy or a generic version). Set it aside.
  • Using a medium-sized mixing bowl and a handheld mixer on medium speed, beat together the cake mix, coffee, milk, vegetable oil, sour cream and vanilla extract. Beat just until combined.
  • Reduce the mixer speed to low. Add the eggs, one at a time, and beat just until all the eggs are incorporated. Scrape down the sides and bottom of the bowl to ensure that the batter is smooth and well mixed.
  • Pour the cake batter into the prepared baking dish and bake for 30 minutes, or until a toothpick inserted comes away clean. Allow the cake to cool for 30 minutes on the counter then place the cake into the freezer while you make the buttercream filling.

Buttercream Filling

  • Using either a stand mixer, or a medium size mixing bowl and a handheld mixer on medium-high speed, beat the softened butter, vanilla extract, and salt for 1 to 1½ minutes, until smooth.
  • Lower the mixer speed to low and add half the powdered sugar and beat to incorporate.
  • Add half the heavy cream, beat for 30 seconds, then add the remaining half of the powdered sugar and heavy cream and beat for an additional 2 to 3 minutes until your buttercream is smooth.
  • Using either a decorator’s bag with a large round tip, or a gallon-size ziploc baggie with a large corner snipped off, fill the bag with the buttercream. The opening of your piping tip, or the size of the hole snipped from the zip-top bag, should be about 1-inch in diameter to get a nice sized line of buttercream when piped.
  • Remove the cake from the freezer. Pipe strips of buttercream down the shorter sides of the cake. Space 1 inch apart. Depending on the thickness of the strips you should be able to pipe 6 strips.
  • Cover the cake and place back in the freezer for 1½ to 2 hours to firm up the buttercream strips.

Chocolate Frosting

  • In a medium-sized saucepan, on medium-high heat, add the light brown sugar, unsalted butter, buttermilk, unsweetened cocoa powder, light karo syrup and salt.
  • Bring the mixture to a boil (this will take about 4 to 5 minutes), making sure to whisk it often so that your frosting doesn’t burn or clump.
  • Once your mixture reaches a rolling boil, then you will want to continue to cook it for an additional 3 to 4 minutes or until your chocolate frosting reaches a temperature of 200 to 210°F on a candy thermometer. Your frosting should start getting thick and should be very smooth.
  • Turn the heat down to low and add your powdered sugar, one cup at a time, whisking until the frosting is smooth. Once all the powdered sugar has been mixed in, add the vanilla extract and turn off the heat.
  • Transfer your chocolate frosting to a large spouted bowl to slightly cool. A 4 cup liquid measuring cup works great for this.
  • Remove the cake from the freezer. Spoon the slightly cooled chocolate mixture over the top of the cake, paying close attention to covering the buttercream strips. You can use a small spatula to carefully smooth the frosting to evenly cover the bumps and cake. Place the cake into the refrigerator for 15 to 20 minutes to allow the chocolate to set-up before slicing and serving.


  • DO NOT use a glass baking dish for this recipe. Since you will be placing a warm cake into a freezer and then also pouring hot chocolate frosting over a frozen cake, you do not want to risk the glass pan being shocked by the extreme changes in temperatures as this can cause the glass dish to crack and break.
  • Do not skip chilling the cake. This is important to ensure it is the right temperature for the next layers to set on top.
  • You do not want to skip the freezing of the buttercream step. This will ensure that when pouring the hot chocolate frosting over the buttercream strips that they do not melt. You do need to remember to work quickly though as the chocolate will start to set up quickly when it hits the cold cake and buttercream.


Calories: 742kcalCarbohydrates: 110gProtein: 6gFat: 33gSaturated Fat: 19gPolyunsaturated Fat: 1gMonounsaturated Fat: 9gTrans Fat: 1gCholesterol: 138mgSodium: 422mgPotassium: 279mgFiber: 2gSugar: 97gVitamin A: 980IUVitamin C: 1mgCalcium: 103mgIron: 1mg