Preheat grill to medium. Mix together cilantro and salt in a small bowl.
Pull back each corn husk, leaving it attached to the cob, and remove the silk. For each ear, cut off a piece of husk, and tie it around the remaining husk to form a bundle.
Grill corn, turning often, until slightly charred and cooked through, about 10 minutes. Serve cobs with butter, and sprinkle with cilantro salt.
Pulling back the husks and tying them into bundles adds a decorative flourish to each ear of corn and gives diners something to hold on to. But doing this is optional. If you prefer, shuck the corn and skip step 2.