Truss the fowl, inserting some pieces of vegetable in the body. Rub breast of bird with lemon, wrap in buttered paper and put in pan with sufficient stock or water to cover. Add remainder of vegetables (sliced), salt and bouquet garni and cook gently until fowl is tender (about 2 hr.). Meanwhile melt butter in a saucepan, add flour and cook without browning; gradually stir in the stock and boil for 10 min., stirring all the time; season. Use some of the liquor from stewpan if no stock is available. Remove trussing string from fowl.
Place on a hot dish, coat with sauce; garnish.