Heat oven to 350° F. Grease and flour two 9-inch round baking pans or one 13x9x2-inch baking pan.
For Cake: Combine sugar, flour, cocoa, baking powder, baking soda and salt in a large bowl. Add eggs, milk, oil and vanilla; beat on medium speed of mixer 2 minutes.
Stir in boiling water and blend well. Pour batter into prepared pans.
Bake 30 to 35 minutes for round pans, 35 to 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.
For Vanilla Buttercream Frosting: In large bowl, beat butter, powdered sugar, milk and vanilla until smooth. Add additional milk, if necessary, 1 tsp at a time until frosting is desired spreading consistency.
Servings: 12