Preheat oven to 350°

Beat egg until frothy

Beat in sugar and melted butter. Cream until light and fluffy.

Add sour cream and vanilla: blend well.

Mix in flour, baking powder, baking soda, and salt. Blend well.

Pour into greased 8" square pan.

Mix together topping ingredients until crumbly. Sprinkle over top of batter.

Bake in oven 25-30 minutes or until done. Serve warm.