BLUEBERRY-GRAPEFRUIT UPSIDE-DOWN CAKES

Steps:

• Heat oven to 350°F (325°F for dark or nonstick pan). Place 1 small piece of butter in each of 24 ungreased muffin cups; place pan in oven until butter is melted. Sprinkle brown sugar evenly over butter. Arrange blueberries on brown sugar.
• Add enough water to grapefruit juice to measure 1 cup. Make cake mix as directed on box, using oil and eggs, substituting grapefruit juice mixture for the water and adding grapefruit peel. Pour batter over blueberries, filling each cup three-fourths full.
• Bake 17 to 22 minutes (20 to 25 minutes for dark or nonstick pan) or until toothpick inserted in center comes out clean. Immediately run small knife or metal spatula around side of each cake to loosen.
• Cool on cooling rack 15 minutes; run knife around sides of cakes again. Place heatproof serving plate upside down over pan; turn plate and pan over. Let stand 5 minutes so topping drizzles over cakes; remove pan. Cool 30 minutes.
• Serve cakes warm or cool with a dollop of whipped topping and sprinkle of cinnamon. Store covered in refrigerator.