Keeping a thin layer of husk on the corn prevents it from burning over the high heat of the grill. If you're using corn that has the husk removed, wrap each cob in a piece of tin foil before putting it on the grill.
Heat grill to high. Remove all but 1 or 2 layers of corn husks (you'll be able to feel and possibly even see the kernels – that's ok!) Place the corn on the grill; cover and cook 10 minutes or until husks are charred. Remove from heat and let cool.
While the corn is cooking, combine the butter, lime juice and zest, cayenne pepper, and salt. Mix well to combine.
When corn is cool enough to handle, peel back the remaining husks and remove the silk (it should come off very easily). If desired, place corn back in the grill for 1-2 minutes to give it some color. Serve with lime-cayenne butter.