Set up the grill for two-zone cooking and heat it to 350 to 400 °F, with one side hotter and one side without direct flame below it. The indirect side should feel steadily hot when the lid is closed, while the direct side is reserved for the crisp finish.

Rinse and scrub the russet potatoes well, removing any dirt from the skin. Dry skins will take on oil and seasoning more evenly than damp ones.

Cut four pieces of 18-inch heavy-duty aluminum foil, or use two layers of regular foil for each potato, then place one potato on each packet. Heavy-duty foil is less likely to tear and leak oil onto the burners or coals.

Drizzle each potato with olive oil, season with salt and black pepper, and wrap each one tightly in foil. The packets should be sealed enough to hold heat around the potatoes without leaving exposed skin.

Place the wrapped potatoes on the indirect side, leaving space between them, close the lid, and cook for 60 minutes. Move and rotate the potatoes at the 30-minute mark so those closer to the hotter zone do not cook faster than the rest.

Use tongs or heat-resistant gloves to carefully remove the foil, then move the hot potatoes to the direct-heat side of the grill. Open the packets away from your face and hands because a burst of steam will escape.

Grill the unwrapped potatoes for 1 to 2 minutes per side, about 4 to 5 minutes total, turning them as the skins brown. The skins should sound slightly hollow when tapped with tongs and yield gently when squeezed.

Check the center of each potato with an instant-read thermometer, aiming for 205 to 215 °F, then transfer to a platter. When split with a knife and fluffed with a fork, the center should release dry steam and break into soft, fluffy flakes.

Open the potatoes, fluff the interiors with a fork, and finish with salt, pepper, and any toppings you like. Serve while the skin is still crisp and the center is hot enough to melt a pat of butter quickly.