Put the lentils in warm water; when reaching a boil, take the lentils out with a skimmer and place them in another pan, covering them with hot salted water.
Bring back to a boil, adding a few sage leaves, the onion and the leeks. Finish cooking. We recommend using broth instead of water. To finish it, add the butter and a little tomato sauce.
“Cooked in the abovemanner, they are served alone or together with rice, potatoes or bread. When passed through a food mill, they become good for soup or for other uses.”