This is from one of my all time favorite cookbooks "Splendid Soups" by James Peterson. From explanation to real tested recipes and a great read as well.
Directions:
1. Cook the meat in a 4 quart pot over medium heat.
2. If you're using bacon, cook the strips until they are just start to turn crisp; if you're using prosciutto, cook it in 2 tablespoons butter because it doesn't have enough fat of its own; if you're using confit, cook the shreds in 2 tablespoons fat.
3. Take the meat out with a slotted spoon, reserve, and leave the fat in the pot.
4. Add the onion, carrot, and celery to the pot and cook over medium heat until the vegetables, brown slightly, about 15 minutes.
5. Add the lentils, bouquet garni, and broth.
6. Simmer until the lentils are tender, 40 minutes to an hour.
7. Discard the bouquet garni and purée the soup with a stick blender, a blender or food processor.
8. Strain it through a fine mesh sieve if you want a finer consistency or add broth or water if you want it thinner.
9. Swirl the 4 tablespoons of butter into the hot soup and add the reserved meat.
Consider adding diced potatoes, garlic, and/or sausage.