Preheat the grill to medium, about 375 to 400°F.
Toss 1/2 pound halved baby potatoes with 1 tablespoon melted butter, 1 minced garlic clove, 1/4 teaspoon salt, and black pepper.
Pile the potatoes in the center of a large sheet of heavy-duty foil. Fold and crimp the edges into a tightly sealed packet, leaving a little room inside for steam to circulate.
Grill the packet for 20 to 25 minutes, flipping once halfway through, until a knife slides easily into the potatoes.
Open the packet away from your face to release steam. Finish with optional 1/2 tablespoon parsley and 1 tablespoon Parmesan.