From The Comfort Table by Katie Lee Joel
2 sticks unsalted butter
1 cup buttermilk
1/2 cup cocoa powder
2 cups flour
2 cups sugar
1 teaspoon baking soda
1/2 teaspoon salt
3 eggs, lightly beaten
1 teaspoon vanilla extract
1 (18 ounce) jar creamy peanut butter (about 2 cups)
8 tablespoons unsalted butter
1/4 cup cocoa powder
6 tablespoons buttermilk
1 (16 ounce) package powdered sugar, sifted
For the cake:
Preheat oven to 350. Grease a 13X9X2 pan.
Place the butter, buttermilk, cocoa, and 1 cup water in a medium saucepan over medium-low heat. Stir constantly until just lightly bubbling. Be careful not to let the milk scorch. REmove from heat and set aside.
IN a large bowl, combine the flour, sugar, and baking soda. Add the eggs and vanilla and stir with a wooden spoon until smooth. Slowly pour in the chocolate mixture and mix well. Pour the batter into the baking pan and bake for about 20 minutes, until a toothpick comes out clean.
While the cake is warm, spoon the peanut butter over the top and gently spread evenly. Let the cake cool until the peanut butter is firm, about 1 hour.
For the frosting:
Place the butter, cocoa, and buttermilk in a medium saucepan over medium low heat. Stir constantly until just lightly bubbling. Remove from heat. Add powdered sugar and mix well. Pour the frosting over the peanut butter, spreading as necessary to cover the top. Let cool until the frosting is firm, about 1 hour.