Cocoa Buttermilk Birthday Cake with Peanut Butter Frosting

Ingredients:

2 cups all purpose flour
½ cup unsweetened cocoa powder
½ teaspoon baking powder
½ teaspoon baking soda
½ teaspoon salt
2 sticks (8 ounces) unsalted butter, room temperature
1 and ½ cups granulated sugar
2 large eggs
2 large egg yolks
1 teaspoon pure vanilla extract
1 cup buttermilk
4 ounces bittersweet chocolate, melted and cooled (optional)

Directions:

Getting Ready to Bake: Center a rack in the oven and preheat the oven to 350 degrees F. Butter two 9-x-2-inch round cake pans, dust the insides with flour, tap out the excess and line the bottoms with rounds of parchment or wax paper. Put the pans on a baking sheet.

To make the cake: Whisk together the flour, cocoa, baking powder, baking soda and salt.

Working with a stand mixer, preferably fitted with a paddle attachment, or with a hand mixer in a large bowl, beat the butter on medium speed until soft and creamy. Add the sugar and beat for about 2 minutes, until it is thoroughly blended into the butter. Add the eggs one at a time, then the yolks one by one, beating for 1 minute after each addition and scraping down the sides and bottom of the bowl as needed. Beat in the vanilla. Reduce the mixer speed to low and add the dry ingredients alternately with the buttermilk; add the dry ingredients in 3 portions and the buttermilk in 2 (begin and end with the dry ingredients); mix only until each new batch is blended into the batter. Scrape down the bowl and, if you want, add the melted chocolate, folding it in with a rubber spatula. Divide the batter between the cake pans.

Bake for 26 to 30 minutes, or until the cakes feel springy to the touch and start to pull away from the sides of the pans. Transfer the cakes to racks and cool for about 5 minutes, then run a knife around the sides of the cakes, unmold them and peel off the paper liners. Invert and cool to room temperature right side up. (Once the layers are cooled, they can be wrapped airtight and left at room temperature overnight or kept frozen for up to 2 months.)

To Assemble the Cake: Place one layer top side up on a cardboard round or a cake plate protected by strips of wax or parchment paper. Frost the top of the layer, and sprinkle the smashed up peanut butter cups inside. Be careful to not overload the inside with peanut butter cups or else it will look uneven when you place the top layer.

Next, cover with the second layer, top side down. Frost the sides and top of the cake, either smoothing the frosting for a sleek look or using a spatula, knife or spoon to swirl it for a more exuberant look. Press the remaining peanut butter cups around the sides of the frosted cake, and if you want you can sprinkle them on top too.

Refrigerate the cake for at least 1 hour (or for up to 1 day, if that’s more convenient) to set the frosting, then bring it to room temperature before serving.

Peanut butter frosting:
from Barefoot Contessa

Ingredients:
1 cup confectioners’ sugar
1 cup creamy peanut butter
5 tablespoons unsalted butter, at room temperature
3/4 teaspoon pure vanilla extract
1/4 teaspoon kosher salt
1/3 cup heavy cream

Directions:
Place the confectioners’ sugar, peanut butter, butter, vanilla, and salt in the bowl of an electric mixer fitted with a paddle attachment. Mix on medium-low speed until creamy, scraping down the bowl with a rubber spatula as you work. Add the cream and beat on high speed until the mixture is light and smooth.