Preheat oven to 350 degrees.
COMBINE in a 13 x 9-inch glass baking dish apples, 4 tablespoons butter, 1/3 cup Splenda, cinnamon, and 1¼ cups water.
COMBINE in a large bowl flour, remaining ½ cup Splenda, baking powder, and salt. Add the remaining stick of butter and milk and beat over medium speed 2 minutes. Add eggs and vanilla and beat 2 minutes more.
POUR and spread batter over apples and bake 35 minutes, or until cake is golden brown. Serve warm with lowfat vanilla ice cream.