My friend Tammy made this for us as a thank you. It was delicious!!!! I made it for us after I asked for the recipe, but it just wasn't the same (I used milk w/ vinegar to make buttermilk instead of using actual buttermilk). She doubled this recipe so it fits in a 9x13.
Cake:
1/3 cup butter, softened
1/2 cup sugar
1/4 cup packed brown sugar
1 egg
1 cup flour
1/2 tsp baking powder
1/2 tsp ground cinnamon
1/2 cup buttermilk
Topping:
1/4 cup packed brown sugar
1/4 cup finely chopped walnuts
1/4 tsp ground cinnamon
Lightly grease an 8" square baking pan. In a bowl, combine, butter and sugars. Add egg. Combine dry ingredients in a separate bowl. Stir the flour mixture into the creamed mixture alternately with the buttermilk. Spread evenly into baking pan.
In a small bowl, combine the topping ingredients. Sprinkle over the batter. Cover, and refrigerate overnight.
The next morning, preheat oven to 350 degrees. Bake the cake for 40-45 minutes in the oven or until a toothpick comes out clean. (Less cooked is better.)