in a large bowl, cream butter and sugar until light and fluffy. Beat in the eggs, sour cream and vanilla. Mix the flour, baking powder, baking soda and salt. Add to creamed mixture and beat until combined. Pour half the batter into a greased 13 x 9" baking pan.
In a small bowl, mix topping ingredients. Sprinkle half of topping over batter. Add remaining batter and topping. Bake at 325° for 40 minutes or until a knife inserted near the center comes out clean. Cool on a wire rack. Makes 12 to 16 servings.