Preheat oven to 350°.
Lightly spoon flour into a dry measuring cup, and level with a knife. Combine the flour and next 5 ingredients (flour through nutmeg) in a bowl, and cut in the margarine with a pastry blender or 2 knives until the mixture resembles coarse meal. Reserve 1/2 cup flour mixture for topping; set aside.
Combine the remaining flour mixture, baking powder, and baking soda, and add the apple juice, vanilla extract, and egg. Beat the mixture at medium speed of a mixer until blended, and fold in the chopped apple.
Spoon the batter into an 8-inch round cake pan coated with cooking spray, and sprinkle the reserved 1/2 cup flour mixture over the batter. Bake at 350° for 30 minutes or until cake springs back when touched lightly in center. Cool the cake on a wire rack.