1. Preheat oven to 350 F.
2. Combine the flour, brown sugar, cinnamon and salt in a bowl, and cut in margarine with a pastry blender until the mixture resembles coarse meal. Reserve 1/2 cup flour mixture for topping and set aside.
3. Combine remaining flour mixture, baking powder and baking soda, and add the buttermilk, vanilla and egg. Beat with a mixer at medium speed until blended.
4. Spoon batter into an 8x8 pan or an 8-inch round cake pan coated with cooking spray. Sprinkle reserved 1/2 cup flour mixture over batter.
5. Bake at 350 F. for 30 minutes or until cake springs back when touched lightly in center. Cool on a wire rack.
2. If you have leftover buttermilk, try the Cinnamon Scones or you can freeze it in ice cube trays and save it for later uses.
Recipe is from Weight Watchers boards. Sorry - I didn't note the original poster, but THANK YOU!!!