1. Heat oven to 350 degrees F. Grease and flour two 9-inch round pans or one 13—9×2-inch baking pan.
2. Stir together sugar, flour, cocoa, baking powder, baking soda and salt in large bowl. Add eggs, milk, oil and vanilla; beat on medium speed of electric mixer 2 minutes. Stir in boiling water (batter will be thin). Pour batter into prepared pans.
3. Bake 30-35 minutes for round pans, 35-40 minutes for rectangular pan or until wooden pick inserted in center comes out clean. Cool 10 minutes; remove from pans to wire racks. Cool completely. (Cake may be left in rectangular pan, if desired.)
Carefully cut each round into 2 layers, so there are 4 cake layers altogether. Use half jar of Hot Fudge on bottom layer of cake, add next cake layer- frost with whipped frosting, add third cake layer- use remaining Hot Fudge, add last cake layer. Frost top and sides with whipped frosting.
Take vegetable peeler and shave both chocolate bars. Carefully coat top and sides of cake.