Debone the meat. Secure it at 1-inch intervals with heavy string. Sprinkle with salt and pepper. Place it over a bed of celery and onion in a roasting pan. Cover with tin foil and roast for 1-1.5 hour until done.
In a saucepan pоur 1.5 l water and add lamb bone, onion, celery, carrots and celeriac diced in big chunks. Let it simmer for 1.5 hours. After that sieve the stock and leave it aside.
Peel carrots and blanch in water until soft but still a bit crunchy. Cut the ends of french beans and blanch in water until done
Dice one shallot, cloves of garlic, little parsley and stir in vinaigrette.
Peel potatoes, wash and place in a baking tray. Pour lamb stock to 1cm. hight. Brush with butter and roast until soft and golden brown.
Make brown Roux and stir in lamb stock. Deglaze the tray from the roasted lamb with wine, sieve and stir in the sauce. Season with salt and pepper.
Slice the meat in 1.5 cm and place it a serving plate. Reheat the french beans, glaze carrots with butter and plate vegetable next to the meat. Add two potatoes and pour the sauce over the meat. See picture.