Peel and trim leek whites, carrot, onion and garlic. Cut them into pieces or slices.
Remove the rind from the bacon and in a large, heavy-bottomed saucepan, brown it until it is a little golden.
Add the chopped vegetables and, over low heat, sweat them for about ten minutes.
Pour in the lentils, stirring to coat with the juices from the bacon and vegetables.
Cover with the broth, bring to a boil, then lower the heat and cook for 45 minutes.
Blend everything together, keeping the texture thick and not too smooth.
While the lentils are cooking, chop the parsley and set aside.
Lightly toast the bread and spread a thick layer of Roquefort cheese on it.
Sprinkle with flat parsley.
Reheat the lentil soup and serve hot with the toast.