You can use fresh or bottled Key lime juice. If Key lime juice is not available, use regular fresh or bottled lime juice.
Garnish each cupcake with a small piece of jellied lime candy slice instead of the lime peel.
If you have only one pan and a recipe calls for more cupcakes than your pan will make, cover and refrigerate the rest of the batter while baking the first batch. Cool the pan about 15 minutes, then bake the rest of the batter, adding 1 to 2 minutes to the bake time.