Rinse the lentils; put them in a large saucepan with about 3 cups of water and bay leaves. Bring to a boil, then reduce to a simmer and cook for 15 minutes. Meanwhile, heat 2 tablespoons of the oil in a large, heavy-bottomed soup pot; add the sausage and brown, stirring frequently. Remove the sausage to a cutting board and cut into 1/4-inch-thick slices. Reserve. Add the remaining oil, the onions and garlic, with a good pinch of salt; cook over medium heat, stirring occasionally, until the onions are soft. Add the celery and marjoram, stirring over medium heat all the while. Add the wine and let it cook until reduced by half. Stir in the lentils with their cooking water, along with the stock, sliced sausage and the carrots; bring to a boil, reduce the heat, and simmer until the lentils are tender and the broth is concentrated, 30 to 45 minutes. Ten minutes before serving, stir in the ketchup, spinach and parsley; simmer for another five minutes. Check for salt and correct. Add freshly ground pepper. Serve with red wine vinegar for guests to add, to taste. Serves 4 with plenty of leftovers.