Boil water and salt and pour into a large enough bowl.
Add cold milk. Sprinkle in puree flakes and stir in briefly. After about 1 minute, mix the puree and stir in the egg yolks. Season with nutmeg. Cut leeks into strips and sauté in hot oil until soft. Sprinkle with pepper and salt. Cut the sausage into small cubes. Mix leek strips and meat sausage cubes into the puree. Divide the mixture evenly into two greased aluminum molds or a gratin dish. Sprinkle breadcrumbs on top and put some butter flakes on top. Bake the potato dish in a heated oven over medium heat for 20-half hours. Serve with a colorful platter of crisp green salads and cool beer.