Cream butter and sugars. Add egg. Mix well. Combine flour, baking powder, baking soda, and cinnamon; add to creamed mixture alternately with buttermilk. Beat well. Spread into a greased 8 in. square baking pan. Combine topping ingredients; sprinkle over batter. Cover and refrigerate overnight. Bake uncovered at 350 for 40 to 45 minutes or until cake tests done.
I usually double the recipe and make it in a 13 x 9 in. pan.
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