Wash the lenses. Put them in the casserole with the piece of broth and cover the lentils with cold water. Add half an onion studded with cloves and the bouquet garni of parsley, bay leaves and thyme.
Simmer covered for 40 minutes. Stir occasionally and add water if necessary.
Cut the chorizo into small cubes and add it to the pot 5 minutes before the end of the cooking time.
Remove the onion and the bouquet garni. Add the truffle mustard.
Homogenize the preparation. Decorate with a few pieces of parsley and serve.