Boil the potatoes in their skins, preferably the day before.
The next day, peel and cut into bite-sized cubes. Add butter and 1 drop of oil to the pan. Then add about 4 tablespoons of breadcrumbs (can be more or less) to the butter, stir with a wooden spoon and lightly roast. Now put the potatoes in the pan, roast them as well and toss them until the desired brown color is achieved.