Cream 1/2 cup butter, 3/4 cup sugar, and vanilla in mixing bowl. Add 3 eggs, beating well. Combine flour, baking powder, and baking soda. Add dry ingredients to butter mixture alternately with sour cream. Set aside. For pumpkin filling, combine pumpkin, 1 egg, 1/3 cup sugar, and pie spice. Set aside. For streusel, cut brown sugar, 1/3 cup butter and cinnamon together until blended. Stir in nuts. Spoon half of batter into a 13x9 baking dish; spread to corners. Sprinkle half of streusel over batter. Spread pumpkin filling over streusel. Carefully spread remaining batter over pumpkin. Sprinkle remaining streusel over top. Bake at 325 degrees for 50-60 minutes or until toothpick comes out clean.