Preheat oven to 350 degrees. Grease bottoms of three 8×9-inch round cake pans and line with parchment or wax paper circle. Grease parchment then coat lightly with small amount of cocoa, tapping out excess. In large bowl, sift together flour, 3/4 cup cocoa, baking soda, and salt. In small bowl, combine buttermilk, coffee, and vanilla extract. In large mixing bowl, beat butter until smooth. Beat in sugar until smooth and creamy. Beat in eggs one at a time, beating well after each addition. Scrape down sides of bowl with rubber spatula; beat again. Alternately add flour mixture in three additions with buttermilk mixture in two additions, beginning and ending with flour mixture. Scrape down sides of bowl; beat again. Pour batter evenly into prepared pans. Bake 20–25 minutes or until wooden pick inserted in center comes out clean. Cool in pans on wire racks for 10 minutes. Invert each layer onto wire rack; remove parchment paper then invert right-side-up. Cool completely. To assemble, level cakes (trim tops off), if desired, using serrated knife. Place dollop of frosting in center of cake pedestal or serving platter. Tear four strips of parchment paper and place in square around outer 3 inches of pedestal. Place one cake layer over dollop of frosting. Spread about 1 cup frosting over top; sprinkle top evenly with about 1/4 cup chopped candy bar. Top with another cake layer; spread with about 1 cup frosting. Sprinkle with remaining chopped candy bar. Top with third cake layer. Cover top and sides with thin layer of frosting. Refrigerate 15 minutes then cover with remaining frosting. With hands, press chopped candy pieces around sides of cake. After frosting has set, gently remove strips of parchment paper. Cut cake into slices to serve.