Preheat oven to 350 degrees F. Spray a 9x9 pan with non stick baking spray.
In a large bowl, cream butter and white sugar. Stir in vanilla, egg, baking powder, and salt.
Alternate stirring in flour and milk until just combined. Do not over mix.
Pour half of batter into prepared pan.
In a small bowl, combine the butter, flour, brown sugar, and cinnamon.
Pour into the batter in pan, and swirl with a knife. Pour remaining batter on top.
In the same small bowl using 2 forks, butter, flour, brown sugar, and cinnamon until mixture resembles coarse crumbs.
Sprinkle topping on top of batter, and press in lightly.
Bake for 40-45 minutes, or until a tooth pick inserted in the center comes out clean.
