Combine topping ingredients, set aside. For cake, cream butter and sugar in mixing bowl. Add eggs, sour cream and vanilla and mix well. Combine flour, baking powder, baking soda and salt. Add to creamed mixture. Beat until combined. Pour half of the batter in a greased 9 x 13 x 2 baking pan. Sprinkle with half of the topping. Add remaining batter, and then topping. Bake at 325° for 40 minutes, or until cake tests done.
Addition: sandwiched a can of peach pie filling in between the layers.