As a first step, preheat the oven to 350°F (180°C). Wash the potatoes well, then wipe them dry.

Prick each potato with a fork in 5–6 places, on all sides.

Rub the potatoes with oil or fat, and coat them with salt on all sides. This is what makes the skins delicious and crispy.

Put the potatoes on a baking sheet lined with parchment paper, and bake for 2 hours. Turn them over roughly halfway through. 20 minutes before the end, turn the temperature up to 425°F (220°C). Don’t forget, the potatoes need to be baked whole, with their skins on.

Take the potatoes out of the oven. With a sharp knife, cut each one lengthwise, very deeply, then make a smaller crosswise cut as well. Open the potato with a knife and fork, and scrape the inside a little with the fork. Be careful, because at this point the potatoes are very hot. Touch the baking sheet only with oven mitts, and handle the potatoes with utensils. But don’t let them cool down, because then they won’t be nearly as delicious.

Place the cold butter, shaved into thin curls with a knife, inside the hot potatoes, and salt them. The hot potatoes will melt the butter, creating a divine flavor combination. Serve immediately.