In a small bowl, combine sour cream and milk; set aside. In a large bowl, cream butter and sugars until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in vanilla. Combine the flour, baking powder, baking soda and salt; add to creamed mixture alternately with sour cream mixture.
Spread two-thirds of the batter into a greased 13-in. x 9-in. baking dish. Combine the filling ingredients; sprinkle over batter. Top with remaining batter.
Bake at 350° for 40-45 minutes or until a toothpick inserted near the center comes out clean. Cool on a wire rack. Yield: 12-15 servings.