Sift together flour, baking powder, salt, and baking soda; set aside.
In large bowl using mixer at medium speed, beat granulated sugar, vanilla, egg, and 1 tablespoon butter until light and fluffy, about 2 minutes. Stir in the Low-Fat Blend until well blended.
Reduce speed to low and mix in dry ingredients until just blended. Don't over mix, or the cake will be tough. Pour batter into greased baking pan.
In a small bowl, stir together brown sugar, cinnamon, and 2 tablespoons flour. Add 2 tablespoons melted butter and mix until crumbly. Sprinkle crumb mixture over batter.
Bake 25 to 30 minutes, or until cake is browned and toothpick inserted in center comes out clean. Cool in pan on rack.