Heat oven to 350°F. Line small muffin cups (1-3/4 inches in diameter) with paper bake cups.
Beat peanut butter, shortening, brown sugar and vanilla in medium bowl on medium speed of electric mixer until creamy. Add egg; beat well. Stir together flour, baking powder and salt; add alternately with milk to peanut butter mixture, beating until well blended. Fill muffin cups 3/4 full with batter; lightly press one mini peanut butter cup into center of each batter-filled muffin cup, leaving chocolate partially uncovered by batter.
Bake 12 to 14 minutes or until top springs back when center is lightly touched. Cool in pan on wire rack about 10 minutes. Remove from pan to wire rack; cool completely. Frost with PEANUT BUTTER CREME FROSTING. Garnish each frosted minicake with mini peanut butter cup or mini peanut butter cup half. About 3 dozen minicakes. For the topping I used buttercream.