To prepare crumbs, combine 3 tablespoons flour and brown sugar in a medium bowl; cut in 1 1/2 tablespoons butter with a pastry blender or 2 knives until mixture resembles coarse meal. Set aside.
To prepare the cake, beat the granulated sugar and the next 7 ingredients (granulated sugar through egg white) with a mixer at medium speed until well blended. Lightly spoon 1 1/4 cups flour into dry measuring cups, and level with a knife. Combine 1 1/4 cups flour, baking powder, soda, and salt in medium bowl, stirring with a whisk. Alternately add the flour mixture and buttermilk to the sugar mixture, beginning and ending with flour mixture; mix after each addition.
Pour batter into a 9-inch round cake pan coated with cooking spray. Arrange apple spokelike on top of batter. Sprinkle with crumb mixture. Bake at 350° for 55 minutes or until a wooden pick inserted in the center comes out clean. Cool in pan for 10 minutes on a wire rack.