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in a small bowl whisk together the mustard, the garlic paste, the chopped rosemary, the chopped thyme, the soy sauce, the wine, and salt and pepper to taste, add 2 tablespoons of the oil in a stream, whisking, and whisk the mixture until it is combined well. Brush the lamb generously on all sides with some of the mustard mixture, and let it marinate in a lightly oil roasting pan, covered and chilled, for at least 6 hours or overnight.Let the lamb come to room temperature and brush it with reserved mustard mixture. In a bowl toss the onions 1 tablespoon of the remaining oil, add the onions and carrots to the pan, and roast them with lamb in the middle of a preheated 450degF oven for 15 minutes.in the bowl toos the potatoes with the remaining 1 tablespoon of oil and add them to the pan. Reduce the heat 350degF and roast the lamb and vegetables, stirring the vegetables occasionally, for 1 hour and 15 minutes, or until a meat thermometer registers 140degF for medium rare meat.Transfer the lamb to a lareg platter and let it stand for 20 minutes. Transfer the onions and potatoes with a slotted spoon to a seving dish, leaving the carrots in the pan, and keep them warm, covered.Make the gravy:Pour off the fat from the pan, add the wine, and deglaze over moderately high heat. Boil the mixture untill it is reduced by half and strain it through a sieve over a saucepan, pressing hard on the carrots.Add the broth and bring the mixture to a boil. In a small bowl knesd together the butter and the flour until it is combined well and add the mixture to the gravy a little at a time, whisking. Add any juices that have accumulated on the platter and salt and pepper to taste and simmer the gravy, whisking occasionally, for 3 minutes, or until it is thickened.Remove the string from the lamb, spoon some of the potatoes and onions around the lamb, and garnish the lamb with the thyme and rosemary sprigs.Serve the lamb, carved with gravy.
