Black and White Marble Sheet Cake with Chocolate Fudge Frosting

If you’re wondering where the Chocolate Fudge Frosting that is supposed to top this cake is, you’ve already seen it in a previous post (and can see it again below), but this shot of the unfrosted cake shows the chocolate and vanilla swirls closeup, in all of their glory.

Backing up, this is a large sheet cake that is perfect for birthdays and other celebrations. The large, flat surface is easy to decorate and the cake can certainly serve a lot of people. In addition to the logistical advantages, a swirled cake is the way to please those who like both chocolate and vanilla . It was moist, with a tight crumb, and had an excellent flavor from butter, sour cream, chocolate and vanilla – a flavor that is best achieved in a homemade cake.

The trick to a good marble cake is not to over-swirl the batter, because that can cause your cake to lose the distinction between dark and light into a medium brown. Swirl a knife through once, making a serpentine through the batter, to get an even marble. If this is too minimal for you, add the batter to the pan in alternating dollops, then swirl the knife through.

The frosting was just amazing. It had a smooth, rich texture and an intense chocolaty flavor. Thick, but not stiff, it ran easily over the top of the cake and set up by itself. Unlike ganache, which could be described in the same way, the creamy chocolate fudge was not heavy. I definitely felt like a kid again when making it – not because I made chocolate fudge frosting as a kid, but because I was tempted to lick the bowl.

Black and White Marble Sheet Cake
1/4 cup sugar
1/4 cup cocoa powder
3 tbsp water, hot
1/2 tsp vanilla extract
2 1/2 cups all purpose flour
1 tsp baking soda
1/2 tsp baking powder
1 tsp salt
1 1/2 cups sugar
1/2 cup butter, softened
2 large eggs
1 tsp vanilla extract
1/2 cup sour cream (regular or low fat)
1 cup milk (whole or low fat)

Preheat oven to 350F and grease a 9×13-inch baking pan.
In a small bowl, combine 1/4 cup sugar, cocoa powder, hot water and 1/2 tsp vanilla extract. Whisk to combine and set aside.
In a medium bowl, whisk together flour, baking soda, baking powder and salt.
In a large bowl, cream together butter and 1 1/2 cups sugar until light. Beat in eggs one at a time, followed by the vanilla and sour cream. Working in two or three additions, alternate adding flour mixture and milk to butter mixture (ending with addition of flour), mixing until no streaks of flour remain.
Scoop out 1 cup of cake batter and stir into cocoa mixture.
Spread white batter into prepared pan. Top with chocolate batter and drag a knife through to create a swirling pattern (don’t over marble, though!).
Bake for 30-35 minutes, until a toothpick inserted into the center comes out clean and the cake springs back when lightly pressed.
Cool completely on a wire rack before frosting.

Chocolate Fudge Frosting
1 cup sugar
1/4 cup cocoa powder
1/4 cup butter, softened
1/2 cup milk (lowfat is fine)
2 tbsp light corn syrup
1/8 tsp salt
2-3 cups powdered sugar
1 tsp vanilla extract

Combine sugar and cocoa in a medium saucepan and whisk until cocoa is dissolved. Add butter, milk, corn syrup and salt, and cook over medium-high heat, stirring occasionally, until mixture comes to a boil (about 10 minutes). Continue boiling; stirring occasionally, for 6 minutes. Remove from heat and cool to room temperature (approx 1 hour). Beat in powdered sugar and vanilla and pour on cake. Frosting will spread easily and will set up itself after a few minutes.