Cream butter in a bowl until smooth; mix in cilantro, lime juice, and cayenne pepper until thoroughly combined. Cover and refrigerate to blend flavors.
Peel husks back from ears of corn, leaving the husks attached at the bottom of the ears. Remove all the corn silk and close husks over the ears again. Cover corn ears with cold water until husks are thoroughly soaked, about 20 minutes.
Preheat grill for medium heat and lightly oil the grate.
Place the corn onto the hot grate and grill covered until husks are charred and the corn kernels are tender, 20 to 25 minutes, turning often. Strip off husks and serve corn with cilantro lime butter.