Cover 1 cup lentils with water. Boil 3 minutes and drain.
Add 6 cups of water (or 3 cups vegetable broth and 3 cups water), 1 large stalk celery finely sliced, 1 large carrot finely chopped, 3 cloves garlic, minced, 1 medium onion, chopped, 1/4 cup olive oil, 1 tsp salt, 1/4 tsp pepper, 3/4 c. tomato sauce, 1 bay leaf.
(I usually enlarge the recipe a bit by using one and a half cup of lentils, 4 cups water, 4 cups broth, 2 stalks celery, 2 carrots, a large onion, and a cup of tomato sauce).
Bring to a boil, cover and simmer one to one-and-a-half hours. Add more water if needed.
Add 2 - 3 T. red wine vinegar (helps to use a really good brand of vinegar), stir, and cook 10 minutes longer.