How to Make It
Preheat oven to 350°F. Grease (with shortening) and lightly flour a 13- x 9-inch pan.
Mix flour, cocoa, baking soda, and salt in a medium bowl; set aside. Beat brown sugar, granulated sugar, and 1 cup butter at medium speed with an electric mixer 2 minutes or until light and fluffy. Add eggs, 1 at a time, beating until well blended. Add melted chocolate and vanilla, beating until blended. Alternately add flour mixture and buttermilk, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Beat in coffee until blended. Pour batter into prepared pan.
Bake at 350°F for 55 to 60 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 to 15 minutes; remove from pan to wire rack, and cool completely (about 1 hour).
Make Peanut Butter Frosting: Beat 1/2 cup softened butter, 1/2 cup creamy peanut butter, and 2 (3-oz.) packages softened cream cheese at medium speed with an electric mixer 2 minutes or until blended. Gradually beat in 1 (16-oz.) package powdered sugar at low speed until blended. Beat in 1 Tbsp. whipping cream and 2 tsp. vanilla. Spread top of cake with frosting.