Let the champagne stand 5 minutes after opening the bottle.
Combine cold water and sugar in a small saucepan. Sprinkle gelatin over sugar mixture; let stand 1 minute. Place pan over medium-low heat; cook until sugar and gelatin dissolve, stirring constantly. Remove mixture from heat; cool slightly. Stir in Champagne.
Spoon 3 tablespoons diced apple into each of 4 (4-ounce) ramekins or custard cups coated with cooking spray. Pour wine mixture evenly over diced apple. Chill 2 hours or until set.
Loosen edges of domes with a knife or rubber spatula. Place a dessert plate, upside down, on top of each ramekin; invert onto plates. Serve with cheddar cheese and apple slices.
Note: You can also remove the domes from the ramekins by quickly dipping the cups in hot water and then running a knife around the edges.