Make our One-Bowl Buttercream Frosting to complete the recipe as show in the image.
Heat oven to 350° F. Grease and flour two 8-inch round baking pans with 2-inch sides and two 6-inch round baking pans with 2-inch sides.
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 pans, filling each pan about 1/2 full.
Bake 30 to 35 minutes or until wooden pick inserted in centers comes out clean. Cool completely in pan on wire rack.
Remove wrappers from peanut butter cups; cut each cup into halves. Set aside.
Prepare One-Bowl Buttercream Frosting; set aside. Loosen cake from pan sides; remove from pans.
To assemble cake, place one 8-inch cake layer on cake plate. Starting in the middle of the cake layer, spread 1/2-inch layer of frosting (about 1-1/2 cups) evenly over surface and just past the edge. Place second 8-inch layer on frosting, pressing gently.
Add about 1/4 cup frosting to center of top cake layer; center one 6-inch cake layer and press gently so that cake layer stays in place. Repeat frosting steps used for first tier. (Use about 3/4 cup frosting between the two 6-inch layers.) Frost entire cake. Place peanut butter cups halves over entire cake. Garnish with peanut butter cup.
*The % Daily Value tells you how much a nutrient in a serving of food contributes to a daily diet 2,000 calories a day is used for general nutritional advice.