Heat oven to 375°F Grease and flour two 9-inch round pans or one 13x9x2-inch baking pan.
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.
Bake 30 to 35 minutes or until tooth pick inserted in center comes out clean. Cool 10 minutes, then remove from pans to wire racks. Cool completely. (Cake may be left in rectangular pan, if desired.).