1 1/2 cups all-purpose flour
1 teaspoon baking powder
1/4 teaspoon salt
1 cup packed light brown sugar
1/2 cup granulated sugar
1/2 cup unsalted butter (at room temperature)
1/4 cup creamy peanut butter
2 eggs
1 teaspoon vanilla extract
1/2 cup chopped unsalted peanuts
24 mini peanut butter cups
1/4 cup semisweet chocolate chips
1 teaspoon butter

Preheat oven to 350 degrees F. Coat a 13 x 9-inch baking pan with nonstick cooking spray.

Stir together flour, baking powder and salt in small bowl. Beat together brown and granulated sugars, butter and peanut butter in large bowl with electric mixer until smooth. Add eggs, one at a time, beating well after each addition. Beat in vanilla extract. Stir in flour mixture to blend. Fold in peanuts. Pour batter into prepared pan. Quarter peanut butter cup pieces and press slightly into batter. Bake for 20 to 25 minutes. Cool in pan on wire rack.

Prepare topping by melting chocolate chips and butter over simmering water in saucepan. Stir until smooth. Drizzle chocolate mixture over bar in pan. Cool. Cut into bars.