PREPARE BATTER: Sift flour with baking powder and salt; set aside. In medium bowl, with rotary beater, beat egg until frothy, then beat in sugar and melted butter until well combined. Add milk and vanilla. With wooden spoon, beat in flour mixture until well combined. Pour into prepared pan. Sprinkle topping evenly over batter. Bake 25 to 30 minutes or until toothpick inserted in center comes out clean. Cool partially in pan, on wire rack. Cut into squares or wedges while still warm. Makes 9 servings.