Heat oven to 350 degrees. Line a 9-inch square
pan with foil; coat foil with nonstick
cooking spray. Prepare Topping: In a
bowl, blend brown sugar, flour, cinnamon
and salt. Work butter into flour mixture
with your fingertips until crumbly.
Refrigerate while preparing cake batter.
Cake: Combine flour, baking powder,
baking soda and salt. Set aside. Beat butter
and sugar until smooth, 2 to 3 minutes.
Beat in eggs, one at a time. Mix in vanilla.
On low speed, beat in half the flour
mixture, the buttermilk and then
remaining flour mixture. Spread half the
batter into prepared pan. Top with
1 cup of the topping, finely crumbling to
cover batter. Top with remaining batter,
spreading to cover topping. Crumble
remaining 2 cups topping over batter.
Bake at 350 degrees for 55 to 65 minutes or
until toothpick inserted in center comes
out clean. Cool in pan on a wire rack.