In large bowl, beat 1/2 cup butter and the granulated sugar with electric mixer on medium speed until light and fluffy. Beat in buttermilk, 1/4 cup rum, the vanilla and egg yolks. On low speed, beat in flour, baking powder, salt and cinnamon. Fold in one-third of the beaten egg whites, then fold in remaining whites. Spoon batter evenly over topping mixture in baking dishes.