1. Heat oven to 350°F. Grease and flour 13x9x2-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 mixer 2 minutes. Stir in boiling water (batter will be thin). Pour batter into prepared pan.
3. Bake 30 to 35 minutes or until wooden pick inserted in center comes out clean. Cool completely in pan on wire rack.
4. Remove wrappers from peanut butter cups; cut each cup into 4 pieces. Prepare ONE-BOWL BUTTERCREAM FROSTING. Reserve 1/3 cup frosting; frost cake with remaining frosting. Sprinkle peanut butter cup pieces over frosting. Place reserved frosting in small microwave-safe bowl. Microwave at MEDIUM (50%) 15 seconds or until pourable; drizzle over cake. Allow drizzle to set. 12 to 16 servings.
ONE-BOWL BUTTERCREAM FROSTING
6 tablespoons butter or margarine, softened
2-2/3 cups powdered sugar
1/2 cup HERSHEY'S Cocoa
1/3 cup milk
1 teaspoon vanilla extract
Beat butter until fluffy in medium bowl. Alternately beat in powdered sugar and cocoa with milk until of spreading consistency (additional milk may be needed). Blend in vanilla. About 2 cups frosting.