Soak whole, unshucked ears of corn in water for a few hours or overnight. Place them over charcoal or in the ashes of a barbecue pit. Rotate the ears about every 5 minutes to avoid burning on one side. They will be ready in about 30 minutes, when the husks are beginning to scorch on all sides and the interior is steaming.
3/4 cup (1 1/2 sticks) butter, softened
2 tablespoons fresh Mexican lime juice
Salt, to taste
Mash butter and lime juice together with a fork. Add salt and blend.