Measure buttermilk and soda in liquid measuring cup; set aside. In large mixing bowl measure flours, sugar and baking powder. Blend. Add egg, oil, vanilla and buttermilk mixture.Stir to blend Topping 1/2 cup lightly packed brown sugar 1 tablespoon cinnamon 1 tablespoon butter Spread half of batter in 9 by 9 inch greased pan and sprinkle with 1/3 of topping; cover with rest of batter. Sprinkle rest of topping onto of the batter. Bake at 350°F for 45 minutes. Cool on wire rack. Submitted by J. Whiser