How to Make It
In a medium bowl, combine the butter, 3/4 cup of chives, 1/2 cup of sour cream and the salt and pepper; mix until smooth. Transfer the butter to a large sheet of plastic wrap and form into a log. Wrap and refrigerate until firm, about 1 hour.
Light a gas grill. Using a sharp knife, slice each potato crosswise at 1/3-inch intervals, cutting down but not all the way through the potato. Cut the chive butter into thin slices, then carefully tuck the butter in between the potato slices. Wrap each potato tightly in aluminum foil.
Set the potatoes on the grill over low heat, cover and cook, turning occasionally, until tender, 45 to 50 minutes. Unwrap the potatoes, garnish with finely chopped chives and serve with sour cream.