Cotechino with Lentils

• 1 cotechino sausage
• ¾ pound brown lentils salt
• ½ Spanish onion

Prick holes in the skin of the cotechino with a fine skewer or the point of a sharp knife. Put cotechino in cold water in a pan just large enough to hold it and bring slowly to the boil. Turn down heat and let the water barely bubble for about 2 hours. While still hot, remove the skin gently and allow sausage to cool. Reserve liquid. When sausage is cool, cut it into fairly thick