Pot-au-feu: Grandma's recipe

This is another traditional, almost grandma's recipe that generations love in France. It is called 'Pot-au-feu'.  It is a dish of  boiled beef cooked over very low heat for a long time in a broth flavored with vegetables and a bouquet garni. Often the broth is served seperately from the vegetables and the beef.

Ingredients (serves 4):
- 500 g lean beef
- A bone marrow
- 4 leeks
- 4 carrots
- 1 stalk of celery
- 2 onions
- 1 clove garlic
- 5-6 potatoes
- 1 bouquet garni (parsley, thyme, bay leaf)
- Salt
- Black peppercorns
Preparation:
Tie the meat for staying in shape during cooking. If there is, cut the oxtail into sections. Peel the carrots, leeks and celery, then wash them.
Place in a pot all the pieces of meat and bone marrow, previously wrapped in gauze to prevent the bone from spreading. Moisten with 5 liters of cold water.
Salt with salt. Bring to a boil, taking care to skim frequently, until no more scum forms.
Add the onions, carrots, leeks (related to boot), celery, garlic and bouquet garni, previously tied. Add 12 peppercorns. Bring back to boil, then simmer, covered (Steam must be able to escape on the side), on low heat for at least 4 hours. 
Remove fat during cooking with a small ladle.
Put your potatoes when the meat  is almost tender. Make sure that you don't overcooked your potatoes and removed it when you have to keep the rest of the dish boiling for more time.
The broth of the pot-au-feu is consumed hot or warm, preceding meats and vegetables alone. It can also be the basis of various soups.
As for the pieces of meat and vegetables, remove from broth and Make them into a hot dish. Serve immediately, with pickles, salt and mustard.