In a large bowl, cream together the butter, granulated sugar, and brown sugar.  Beat in the egg until well blended.  In a medium bowl, combine the flour, baking powder baking soda, and cinnamon.  Stir the flour mixture into the creamed mixture alternating with the buttermilk.  Spread into a lightly greased baking pan (approx 8 inches).

Topping:

1/4 cup packed brown sugar

1/4 cup finely chopped walnuts

1/4 tsp ground cinnamon

In a small bowl, mix brown sugar, walnuts and cinnamon.  Sprinkle over the batter.  Cover and refrigerate over night.

Preheat oven to 350 degrees.  Bake 40 to 45 minutes or until a toothpick inserted comes out clean.