Preheat the grill to 390°F (200°C) for 15 minutes.
Scrub and wash the potatoes, and pat them dry with paper towels.
Pierce the potatoes with a fork a couple of times on each side to allow heat to escape.
Brush the potatoes with any neutral oil that has a high smoke point (such as avocado or grapeseed oil), and season with sea salt.
Wrap each potato individually in 2 layers of foil.
Place the wrapped in foil potatoes directly on the grill, and cover with the lid. Cook for 45-55 minutes turning halfway through, or until you can easily pierce the center of a potato with a knife or a fork. If you have a kitchen thermometer, the internal temperature should be around 205°F (95°C).
Using kitchen tongs, remove the hot potatoes from the grill and allow them to cool down a little so that you can handle them with your hands.
Unwrap foil, and cut the potatoes open immediately with a knife as otherwise they'll steam inside and become heavy.
Add a piece of butter, and lightly fluff with a fork then serve with your favorite toppings!