- Prep Time: 45 min
- Cook Time: 45 min
- Total Time: 1 hr 30 min + 3 hr freezing time
- Yield: 10 servings
- Category: Dessert
For the cake:
- 2 cups sugar
- 2 cups flour
- 1 cup water
- 1/2 cup vegetable oil
- 1/2 cup butter
- 3 tablespoons sweetened dark cocoa powder
- 3 large eggs
- 1/2 cup buttermilk
- 1 teaspoon baking soda
- 1 teaspoon vanilla extract
For the frosting:
- 8 tablespoons butter, slightly softened
- 3 tablespoons whole milk
- 1/2 teaspoon vanilla extract
- 2 cups powdered sugar
For the 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 dark cocoa powder
- 1/3 cup light corn syrup
- 1/4 teaspoon salt
- 16 tablespoons unsalted butter, cut into tablespoon-sized pieces, divided
To prepare the cake:
- Preheat oven to 350 degrees F.
- Butter and flour a 9×13-inch pan, and set aside.
- In the bowl of a stand mixer fitted with a paddle attachment, combine sugar and flour on low, and set aside.
- In a medium saucepan over medium-high heat, bring water, oil, butter and cocoa to a boil. Stir until smooth.
- Pour butter-cocoa mixture into the flour mixture. Beat on medium low for about a minute. Add eggs, buttermilk, baking soda and vanilla. Beat on medium for an additional minute. Spread cake batter into prepared pan, and bake until a cake tester comes out clean, about 30 minutes.
- Allow cake cool completely on a wire rack. Cover cooled cake, and chill in the freezer for a at least an hour up to overnight.
To prepare the buttercream frosting:
- In the bowl of a stand mixer fitted with a paddle attachment, beat butter, milk and vanilla on medium low speed. Reduce speed to low. Carefully add powdered sugar, beating until just mixed. Increase speed to high, and beat mixture until smooth.
- Using a large round piping tip, pipe frosting in lines across the surface of the cake, about 1 inch apart.
- Return cake to the freezer for an hour.
To prepare the fudge frosting:
- In the bowl of a stand mixer fitted with a whisk attachment, mix the buttermilk, powdered sugar and vanilla on low.
- In a medium saucepan, combine sugar, cocoa, corn syrup, salt and 8 tablespoons of the butter. Stir to incorporate butter. Bring mixture to a boil over medium high heat. Cook until mixture registers 240 degrees F on a candy thermometer. Remove from heat.
- While whisking constantly, add hot mixture to buttermilk mixture. Add remaining 8 tablespoons of butter. Continue whisking until fully incorporated. Allow mixture to cool to lukewarm.
To assemble the cake:
- Remove the cake from the freezer. Pour fudge frosting to cover the buttercream rolls.
- Using an offset spatula, cover the buttercream rolls and the surface of the cake in a thin sheet of fudge.
- Return the cake to the freezer for at least an hour before serving.