Cut the onions fine and brown them in the butter. Wash the lentils then add them to the broth with the salt, tomato sauce or chopped tomatoes. Cook approximately 30 minutes.

Serve with small bread pieces fried in butter.

NOTE: After the soup is cooked you can add some finely chopped parsley. Some chefs serve this soup after blending it in an electric mixer, or passing it through a food mill; and adding some flour.