2) Place the lamb in a roasting pan with the ribs curving down, and coat the tops with the mustard mixture. Allow to stand for one hour at room temperature. Preheat the oven to 230°C / gas mark 8.
3) Roast the lamb for exactly 20 minutes for rare or 25 minutes for medium-rare. Remove from the oven and cover with aluminium foil. Allow to sit for 15 minutes, then cut into individual ribs and serve.
Note: French trimming refers to scraping the meat off the tips of the bones. Ask your butcher to leave 1/2cm of fat on the meat.