Stir together the flour and baking soda. Set aside.
In a large bowl, beat together the sugar, butter, egg, and vanilla until smooth. Add flour mixture and sour cream alternately to beaten mixture; beat smooth.
Transfer to a greased and floured 15x10x1-inch baking pan. Prepare Crumble Topping; sprinkle over top. Bake in a 350 degree F oven about 20 minutes or until a wooden toothpick inserted near center comes out clean. Cool on a wire rack for a few minutes. Serve warm. Makes 15 to 20 servings.