Preheat grill to medium.
With a fork prick the potatoes 4 to 5 times, smear them with a little butter and sprinkle each potato with salt. Wrap in foil. Place the potatoes on the grill and cook for 40 to 45 minutes turning every so often.
In a mixing bowl add butter, garlic, chives and pepper. Whip together until well incorporated. Take a piece of plastic wrap and lay it on the counter. Place the butter mixture on the plastic wrap and shape into a log or place the bowl in refrigerator covered to firm it back up. When your potatoes are cooked take butter out of the refrigerator, slice open the potatoes and top with herb butter.