Preheat oven to 350^. Grease the bottom and corners of 9-inch loaf pan (I sometimes use two 8- inch loaf pans and they turn out great-I like this way)Cut and fold foil to fit in pan and hang over ends of pan, for easy removal after baking. Spray foil , but not sides of pan (not spraying sides makes bread rise nicely). Turn temperature to 325^ if using dark pans or glass.
In a large mixer bowl beat margarine and sugars together until combined and fluffy. Add eggs, and vanilla. If using the lemon or vinegar mixture mix it up now and set aside. Combine flour,and remaining dry ingredients (sprinkle a fit of this flour mixture over apples-set aside) and add remaining flour mixture alternately with the buttermilk. Blend after each addition. Remove bowl from mixer and stir apple mixture and nuts in by hand just to incorporate. Spoon batter in prepared pan or pans;spreading evenly. Sprinkle topping over batter and bake for 50 to 60 minutes testing with toothpick for doneness. Let rest in pan or pans for 5 minutes, then run a table knife inside pans around sides to loosen. Carefully lift out bread by the overhanging foil. Place on wire rack to cool completely before slicing.
In a small bowl combine the brown sugar and spices with the flour. Using a pastry blender cut the butter in until coarse crumbs form. Stir in nuts. Sprinkle on top of bread loaf or loaves and bake.