Peel the potatoes and dice them very small. Cut the leek into slices and sauté briefly. Bring 1 liter of water to the boil and dissolve the meat stock in it. Then add the leek and potatoes. Then cook the whole thing until the potatoes are tender.
Dice the sausage in between.
Remove the saucepan from the heat, add the crème fraîche, stir and season with salt and pepper. Finally add the sausage.