Sweat the butter and shallot cubes in a saucepan and add the drained lentils. Season with pepper, pour on the stock and simmer for about 30 minutes until the lentils are cooked through. There should be no more stock in the pot.
Cut the two shallots into strips. Fry the diced bacon until crispy, fry the shallots briefly. Deglaze with the vinegar, season with salt and pepper. Add the cooked lentils, heat everything well. Add the butter and parsley. To taste.