Bumpy Cake is a Detroit tradition. This moist, dark chocolate cake has a sweet layer of buttercream topped with a fudgy, almost caramelly chocolate frosting. It's ideal for chocolate lovers, and though it has three separate components that require freezer cooling to obtain picture perfect results, it's well worth the effort.
Note: This cake does very well right out of the freezer. Freezing the cake before piping the buttercream, then freezing the piped cake before pouring the frosting on, is essential to harden the buttercream enough for the frosting to properly adhere.
This recipe is adapted from a Sanders' recipe published some years ago in a Detroit newspaper and accessed via Food.com.
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- For the Cake
- 1 tablespoon unsalted butter
- 1/2 cup plus 2 tablespoons unsweetened Dutch process cocoa powder
- 1/2 cup hot black coffee
- 1/2 cup canola oil
- 1 cup buttermilk
- 1 tablespoon pure vanilla extract
- 1 1/2 teaspoons baking soda
- 1/2 teaspoon salt
- 2 eggs, lightly beaten
- 3/4 cup dark brown sugar, firmly packed
- 3/4 cup white sugar
- 2 cups all-purpose flour
- For the Buttercream Frosting
- 1/4 cup unsalted butter
- 1/4 cup vegetable shortening
- 2 1/2 cups confectioners sugar
- 1 teaspoon vanilla extract
- For the Pourable Fudge Frosting
- 1/2 cup buttermilk, room temperature
- 2 1/2 cups powdered sugar
- 1 teaspoon vanilla extract
- 1 cup sugar
- 1/3 cup unsweetened Dutch process cocoa powder
- 1/3 cup dark corn syrup
- 1/4 teaspoon salt
- 16 tablespoons (2 sticks) unsalted butter, cut into tablespoon-sized pieces
Set oven rack to the middle position and preheat oven to 375°F. Grease a 9- by 13-inch pan or baking dish with butter. Add 2 tablespoons cocoa powder to pan and shake and tap pan gently until the butter is completely coated in cocoa. Tip out excess.
In the bowl of a stand mixer, combine cocoa and coffee, beat on medium speed for 30 seconds. Add oil, beat for 30 seconds; add buttermilk, beat for 30 seconds; add baking soda, beat for 30 seconds; add salt, beat for 30 seconds; add vanilla, beat for 30 seconds; add eggs, beat for 30 seconds; add sugars, beat for 30 seconds. Add flour and beat about 5 minutes to remove any lumps. Batter may begin to bubble.
Pour batter into prepared pan and use spatula to smooth top. Bake until cake tester comes out clean, 35 to 40 minutes. Transfer to a rack and allow to cool for at least 30 minutes. Transfer to the freezer for at least an hour and up to overnight.
For the Buttercream: In the bowl of a stand mixer fitted with a paddle attachment, cream together butter and shortening on medium speed until light and fluffy, about 3 minutes. Add confectioners’ sugar and mix to fully incorporate, about 1 minute. Add vanilla extract and mix until blended, about 30 seconds. Transfer frosting to a piping bag fitted with a large round tip. Refrigerate for at least 15 minutes to firm up frosting.
Pipe frosting crosswise into seven 1-inch wide lines spaced 1-inch apart (each "bump" should run the length of the cake, 9-inches long). Return cake to the freezer for at least 30 minutes to set the frosting.
For the Fudge: In a large bowl whisk together buttermilk, confectioner's sugar and vanilla and set aside. In a medium saucepan, combine, sugar, cocoa, corn syrup, salt and 1 stick worth of butter. Stir occasionally to fully incorporate butter as it's melting then bring mixture to a boil over medium high heat.
Cook until mixture registers 240°F on a candy or instant read thermometer (a small amount dropped into cold water should form a soft, malleable ball), then remove from heat. While whisking constantly, add hot mixture to buttermilk mixture. Add remaining butter pieces and continue whisking until fully incorporated and mixture has cooled (frosting must be only slightly warm).
Remove frosted cake from freezer and pour cooled frosting over the cake in long strokes to cover buttercream rolls completely. Note: frosting will be thin and saucelike. Working quickly and evenly you'll be able to completely cover the bumps with a thin layer of frosting, while "frosting runoff" will create fudgy pockets along the surface beside the bumps that will firm up in the freezer. Return cake to freezer for at least 30 minutes more to set. A smaller, paring knife is most effective for cutting while maintaining the cake's unique look. Serve chilled and store leftovers in refrigerator or freezer.