Soak one cup of lentils over night. Drain and boil slowly for one hour
in water containing one-half teaspoon of baking soda, drain and boil
again very gently in fresh water; when the lentils are tender drain off
most of the liquid and return to the fire. Add two tablespoons of
butter, or butter substitute, two teaspoons of salt, and one-half
teaspoon of sugar. Bring three cups of milk to a boil in the
double-boiler. Just before serving mash the lentils through a strainer
directly into the milk. Serve in cups and pass croutons with the soup.