Butterscotch Bars

Preheat the oven to 350 degrees.Beat the sugar and butter on a medium speed mixer until smooth (about 4 minutes). Add egg whites and vanilla; beat well. Lightly spoon the flour into dry measuring cups and smooth with a knife. Combine flour, baking powder, and salt; whisk well. Add the flour mixture to the sugar mixture; beat on low speed until smooth.Spread the dough evenly on an 8-inch square baking dish covered with cooking spray; sprinkle evenly over the pieces. Bake at 350 ° C for 28 minutes or until a wooden stick inserted in the middle comes out clean. Cool in the pan on a wire rack.