Heat oven to 350°F Line bottom of two 9-inch round pans with wax paper.
Combine sugar, flour, cocoa, baking soda, baking powder and salt in large bowl. Add milk, eggs, oil and vanilla; beat on medium speed of mixer 2 minutes. Stir in boiling water. (Batter will be thin.) Pour into prepared pans.
Bake 18 to 22 minutes or until wooden pick inserted in centers comes out clean. Cool 10 minutes; remove from pans to wire racks. Carefully remove wax paper. Cool completely.
To assemble dessert, place one cake layer on serving plate. Spread with half of whipped topping; top with half of pie filling. Top with second cake layer. Spread with remaining topping and pie filling. Refrigerate at least one hour.