Sift flour, baking powder, salt and cinnamon onto wax paper. Melt butter in a medium-size saucepan over moderate heat. Remove from heat. Beat in sugars, egg and vanilla with a wooden spoon until smooth. Stir in flour mixture, apple and walnuts until thoroughly combined. Spread into a greased 8x8x2-inch pan. Sprinkle with 1 tablespoon of the cinnamon-sugar mixture. Bake in a moderate oven (350°) for 30 minutes, or until top springs back when lightly pressed with fingertip. Cool completely in pan on wire rack. Cut into squares. Cinnamon Sugar: Combine 1/2 cup granulated sugar with 1-1/2 teaspoons ground cinnamon in a small jar with a screw-top lid. Cover; shake thoroughly. Store remainder for future use (for french toast, pancakes, fruit-topped desserts, etc.). Turn these into blueberry squares by substituting fresh or frozen berries for apple. bake 20