Peel the potatoes, and cut off the tops and bottoms to give a flat surface.
Cut the butter into 1cm slices and lay in a frying pan. Lay the potatoes on top of the butter and season with salt.
Pour in enough water to so that it’s just below the surface of the potatoes. Open up the butter paper and lay on the potatoes.
Place the pan on the hob and bring to the boil. Simmer the potatoes gently in the butter and water.
Let the potatoes simmer hard in the butter until they are evenly and deeply browned on one side and then flip them. Season with more salt.
Once cooked through remove them from the heat and cover in a double layer of cling film. Leave the potatoes off the heat to rest in the butter for about an hour.
Finish by brushing the potatoes with a little of their own butter juice, then check if they need more salt.