Soaking the lentils of the night in the water. Chopped onion and stew it with the butter in a large saucepan. Then pressed clove of garlic and a little stew with onions. Put the pan in the lentils, pour 2 liters of water and leave to simmer on low heat (until lentils soften - about 30-40 minutes). Finally chop the celery into cubes and put it together with the chopped parsley into the pan. Leave to choke 6-7 minutes. Subtract from the pan half of the lentils, and blend it back into the pan. Cut sausage into slices and add to the pan. Once the dish boil, serve.