Wash the lentils well in cold water, put them over the fire, in four quarts of cold water with the drippings, salt, and pepper, and boil slowly until tender, that is about three hours; drain off the little water which remains, add to the lentils the butter, parsley, sugar, and a little more salt and pepper if required, and serve them hot. Always save the water in which they are boiled; with the addition of a little thickening and seasoning, it makes a very nourishing soup.
The Cooking Manual of Practical Directions for Economical Every-Day Cookery (1877).