01 - Preheat grill to medium-high heat, approximately 400°F.
02 - Wash and scrub potatoes thoroughly. Place each potato between two wooden spoons or chopsticks and slice crosswise at 1/8-inch intervals, cutting nearly to the bottom without slicing all the way through.
03 - In a small bowl, combine melted butter, minced garlic, chopped parsley, thyme leaves, kosher salt, and black pepper. Stir until well blended.
04 - Brush the garlic herb butter generously over each potato, ensuring the mixture seeps between the slices for even flavor distribution.
05 - Wrap each potato loosely in a double layer of aluminum foil, leaving the top slightly open to allow crisping during cooking.
06 - Place foil-wrapped potatoes directly on the grill, cover, and cook for 35 to 40 minutes, brushing occasionally with remaining garlic butter. Remove foil for the last 5 to 10 minutes to achieve a crispy golden exterior.
07 - Transfer potatoes to a serving platter. Sprinkle with grated Parmesan cheese and chopped chives. Serve immediately while hot.