In a large bowl, beat the sugar, buttermilk, coffee, eggs, oil, chocolate and vanilla until well blended. In another large bowl, combine the flour, cocoa, baking soda, baking powder and salt; gradually beat into buttermilk mixture until blended.
Pour into three greased and floured 9-in. round baking pans. Bake at 350° for 30-35 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes before removing from pans to wire racks to cool completely.
For frosting, combine the cream, sugar and corn syrup in a small saucepan. Bring to a full boil over medium heat, stirring constantly. Remove from the heat; stir in chocolate and butter until melted.
Transfer to a large bowl. Cover and refrigerate until desired consistency, stirring occasionally. Spread frosting between layers and over top and sides of cake. Store in the refrigerator.