Heat oven to 350°F. Grease and flour two 9-inch round baking pans, or three 8-inch round baking pans.
Stir together sugar, flour, cocoa, baking powder, baking soda and salt in a large mixer bowl. Add eggs, milk, oil and vanilla; beat on medium speed of mixer for 2 minutes. Mix in boiling water - the batter will be quite thin. Pour batter into prepared pans.
Bake 30 to 35 minutes or until wooden pick inserted in center comes out clean. Cool 10 minutes on a wire rack, then tap the cakes out of the pans. Cool completely before frosting.
