In a large stockpot place 6 leeks, 6 carrot pieces, 6 celery pieces and onion. Tie each piece of meat individually to hold its shape during the long cooking time, and place on top of the vegetables. Add 2 marrowbones to the pot, tucking them between the meat, and the bouquet garni, salt and peppercorns. Add enough water to cover and bring to a boil over high heat. Reduce the heat and simmer partially covered for 3 hours, skimming any foam which forms on the top.

Strain the broth and discard the cooking vegetables. Return the broth and meats to the pot and add the bay leaves, and the remaining marrowbones and vegetables except the potatoes. Bring the broth to a simmer and cook, partially covered, for 1 hour, adding the potatoes after a 1/2 hour.

Remove the meat from the broth and discard the trussing strings. Carefully remove the vegetables from the broth, place them on a large serving platter, and moisten with some broth. Cover and keep warm.

Strain the broth and discard any remaining vegetables. Carve the meat and place on the serving platter with the vegetables. Cover and keep warm.

Rub the bread with garlic and lightly toast before placing in the bottom of a shallow bowl. Pour equal amounts of broth over the croutons and serve as a first course. Pass the marrowbones at the table and serve with additional toast for spreading the marrow. Serve the meat and vegetables as a main course with desired condiments.