Cream butter, 3/4 cup sugar and vanilla in mixer bowl.
Add 3 eggs, beating well after each.
Combine flour, baking powder and baking soda.
Add dry ingredients to butter mixture alternately with sour cream.
Combine pumpkin, beaten egg, 1/3 cup sugar, and pie spice.
Spoon half of cake batter in 13 x 9 x 2 inch baking dish.
Spread to corners.
Sprinkle half of Streusel over batter
Spread pumpkin mixture over Streusel.
Carefully spread remaining batter over pumpkin mixture.
Sprinkle remaining Streusel over top.
Bake in slow oven (325 degrees F) 50-60 minutes or until toothpick inserted in center comes out clean.