Mix together oatmeal, flour, brown sugar, vanilla, baking powder and salt. Work in butter to crumb topping.
1 1/2 cups oatmeal, 1 1/2 cups flour, 1 1/2 cups firmly packed brown sugar, 1 teaspoon vanilla extract, 1 teaspoon baking powder, 1/2 teaspoon salt, 2/3 cup butter