1. In a large bowl, cream butter and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in buttermilk and vanilla. Combine the flour, baking powder, salt and baking soda; gradually add to creamed mixture. Fold in apples and walnuts. Pour into a greased 9-in. x 5-in. loaf pan.
2. For topping, combine the sugar, flour and cinnamon. Cut in butter until mixture resembles coarse crumbs. Sprinkle over batter.
3. Bake at 350° for 55-60 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes before removing from pan to a wire rack. Yield: 1 loaf (16 slices).