Preheat oven to 400 degrees F.
Coat each ear of corn in 2 tablespoons of the cilantro lime butter and wrap individually in foil. Roast until hot and steaming, about 25 minutes. Serve with extra butter on the side.
Put the butter in a mixing bowl and, using a rubber spatula, mix in the cilantro, lime zest, lime juice, salt and cayenne. Use immediately or refrigerate.