Prepare cake as directed on package with water and butter. Pour batter into greased or paper-lined muffin cups. Bake at 325° for 40-45 minutes. Place chocolate chips and half the Cool Whip in bowl; microwave on high 1 minute or until chips are melted. Stir every 20 seconds. Fold in remaining Cool Whip, cinnamon and rum or vanilla. Cover; refrigerate 30 minutes. Frost cooled muffins. Makes about 12 muffins.