Chocolate Peanut Butter Cup Cake

The original recipe for this is intended for a 3 layer cake, with generous frosting and filling between layers. And it's indeed spectacular. But it's very rich, and most of the time I'm making it for a crowd, so I adapted the recipe to make a sheet cake instead. If you have leftovers of peanut butter icing or ganache, they freeze very well, or can be used on any cupcake or brownie recipe. 

There are 3 main components: the cake, the peanut butter icing, and the chocolate ganache. Start the cake early in the day or the night before so it can cool completely before finishing. I often freeze my cakes before icing or filling, since it gives a much cleaner result. 

Cake

1 2/3 cups flour

2 cups sugar

2/3 cup cocoa

2 tsp baking soda

1 tsp baking powder

1 tsp salt

2 eggs

1 cup buttermilk

1/2 cup oil

1 Tbsp vanilla

1 cup strong hot coffee (instant in boiling water is fine)

Grease and flour a 9X13 or 10X15 cake pan. Preheat oven to 350F. Put all dry ingredients into a mixing bowl or stand mixer bowl. Stir together til homogenous. Add in eggs, buttermilk, oil, and vanilla and beat until blended. Scrape down bowl. Add hot coffee and beat in at low speed (so that you're not splashed with hot coffee). Once it's mostly incorporated, turn mixing speed up to medium and beat for 1 minute. Scrape down bowl and beat another 30 seconds. Batter will be very thin. Pour into prepared pan. Baking time will vary, depending on the size of pan you used. Start checking at 20 minutes, but it could take up to 35 to 40 minutes. It will spring back when pressed lightly, and a toothpick inserted in the centre of the cake will be mostly clean, but will have a few moist crumbs. It should not have wet batter, though. Cool completely before icing. 

Peanut butter icing

1 cup icing sugar

1 cup peanut butter

1/4 cup butter

1/3 cup whipping cream

1 tsp vanilla

1/4 tsp salt

Cream butter and peanut butter together. Add the rest of the ingredients and beat until fluffy. Taste and add more salt if necessary (different brands of peanut butter are salted differently). Add more icing sugar or cream to get a thick, soft, fluffy icing. Ice the cooled cake and refrigerate. 

Chocolate ganache

2/3 cup chocolate chips (mini is best)

1/3 cup whipping cream

Put the chocolate chips in a bowl. Heat the cream in a small saucepan just to boiling - cream will start to steam and tiny bubbles will form on the edges. Take off heat and pour over the chocolate chips. Let stand for two minutes. Whisk gently, starting from the middle and moving to the edges to incorporate cream and chocolate into a smooth mixture. Set aside til room temperature and thickened but pourable, whisking occasionally. 

When the cake and icing have cooled, pour the ganache over the icing in a thick drizzle. Top with chopped peanut butter cups and refrigerate to set the ganache before serving. Store leftovers in fridge. 

Here's a shot of the triple layer version I made for my father in law's birthday several years ago. Unfortunately, I didn't get a picture of the cross section, but it looks great with the layers of peanut butter filling between the dark chocolate cake. Ingredient amounts for the layer cake version below.

For a 3 layer cake:

Cake

2 1/2 cups flour

3 cups sugar

1 cup cocoa

3 tsp baking soda

1 1/2 tsp baking powder

1 1/2 tsp salt

3 eggs

1 1/2 cups buttermilk

3/4 cup oil

1 1/2 Tbsp vanilla

1 1/2 cups strong hot coffee

Bake as above in 3 X 8 inch round pans. 

Peanut butter icing

2 cup icing sugar

2 cup peanut butter

1/2 cup butter

2/3 cup whipping cream

2 tsp vanilla

1/2 tsp salt

Ice between each layer, and top and sides of cake. 

Chocolate ganache

1 1/3 cups chocolate chips

3/4 cup whipping cream

Pour ganache on top of cake, letting it drip down the sides. It will not cover the sides entirely, some peanut butter icing will be showing.