1. Preheat oven to 350°.
2. Coat a 9-inch round cake pan with cooking spray, and dust with 1 tablespoon flour.
3. Weigh or lightly spoon 6.75 ounces flour into dry measuring cups; level with a knife. Combine 6.75 ounces flour, baking powder, salt, and cinnamon in a small bowl, stirring with a whisk. Place granulated sugar and butter in a large bowl; beat with a mixer until well blended. Beat in vanilla and egg. Beat in flour mixture alternately with milk, beginning and ending with flour mixture. Fold in apple, raisins, and walnuts. Scrape batter into prepared pan. Bake at 350° for 30 minutes or until a wooden pick inserted in center comes out clean. Cool 10 minutes in pan on a wire rack. Remove from pan; cool completely on wire rack. Sift powdered sugar over cake. Cut into wedges.