Preheat oven to 350°. Line 8-inch baking pan with aluminum foil, then spray with nonstick cooking spray; set aside.
Blend flour with baking powder in medium bowl; set aside.
Beat Spread with sugar in large bowl with electric mixer on medium speed 2 minutes or until light and fluffy. Add egg and banana and beat on low speed until well blended. Beat in flour mixture just until blended. Spread into prepared pan, reserving 1/2 cup batter. Mix Skippy® Creamy Peanut Butter into reserved batter. Evenly spread peanut butter mixture on cake batter, then gently swirl with butter knife to marble.
Bake 35 minutes or until toothpick inserted in center comes out clean. Cool on wire rack. Sprinkle, if desired, with confectioners sugar, then cut into 16 squares. Serve with Breyers® Ice Cream.