In a large bowl, combine the sugar, flours, baking powder, salt and cinnamon. In a small bowl, whisk egg and vanilla. Stir into dry ingredients just until moistened. Fold in apples and walnuts., Transfer to a 9-in. pie plate coated with cooking spray. Bake at 350° for 25-30 minutes or until a toothpick inserted in the center comes out clean. Sprinkle with confectioners' sugar if desired. Serve warm.