Peel the potatoes as neatly as possible, making them as round as you can. In salted water, over medium heat, bring them slowly to a boil. Cook for 15 minutes in barely simmering water, then let them cool slightly. You can also cook the potatoes in their skins. In that case, bring them slowly to a boil and cook them for 15 minutes in barely simmering salted water, then let them cool slightly. Cool the potatoes with cold water, then use a sharp knife to pull off their skins. Try to remove the skins as neatly as possible so each potato stays round. Set the potatoes aside. It is important that by the time you put the potatoes into the caramel, they are completely dry.

Sprinkle the sugar evenly into a cold skillet. Start heating it over medium-high heat. Do not stir or shake it while it heats. When it begins to melt, reduce the heat to medium and cook until the caramel turns golden brown. You must not stir the caramel while it is cooking, because it will crystallize. Wait patiently until it is evenly brown. If the surface of your skillet is not even—which is not good, but it happens; mine was like that too—then carefully move it with a spatula once most of it is already liquid and browning.

Turn the heat down to the lowest setting, or if you have an electric cooktop that holds heat, turn it off. Carefully pour in the cold water from close to the pan and stir it in. Add the butter and stir that in as well, until it has completely melted.

Pour the potatoes into the skillet, into the caramel. Carefully, so you don’t scald yourself, start shaking the pan until the potatoes are completely coated in the caramel.