Carefully clean the leeks, cut away the root end and cut into rings a good 1 cm wide.
Heat the butter in a large frying pan and add the leeks. Add a little water and cook the vegetables on a low heat for ten to fifteen minutes, stirring occasionally.
At the same time as preparing the leeks, put the saucissons in a frying pan, cover with cold water, bring to the boil and cook for 35-45 minutes, depending on their size, before reaching the boiling point (water must not be allowed to do anything, otherwise the sausage will burst!).
Peel the potatoes and cut into cubes. After ten min cooking time add to the leek form. Add the white wine, season with salt and pepper and simmer for another 20-25 minutes with the lid closed.
Spread the cooked vegetables evenly in a baking dish. Cut the sausage into slices and put them into the leek vegetables. Sprinkle everything with the cheese.
Meanwhile, bake the leek papet in the oven heated to 220 degrees on the lowest rack for twelve to fifteen minutes.