Simmer the lentils gently in three pints of water for one and a half hours. Strain. Put a quarter of a pound of the lentils on one side to cool. Rub the rest through the wire sieve with a wooden spoon until nothing but the skins remain. In the meantime, boil the vegetables with sufficient water to cover, until quite tender. When thoroughly cooked pour into the lentil purée, add the sauce and salt, and re-warm. Prepare forcemeat, adding the quarter of a pound of lentils chopped fine; shape into little cutlets (about twelve), brown in a frying-pan with the butter, place on a hot dish, pour the gravy over, and serve at once.