Make little slits in the meat and insert garlic and rosemary. Mix the mustard, soya sauce and pepper and spread over the leg. Sprinkle generously with whole rosemary. Cover and let marinate a few hours in the refrigerator.
Heat the oven to 425 °F/220 °C.
In a baking dish, make a bed of onions, place the leg on top and add in the stock.
Cook for approximately 20 minutes, then cover and reduce the heat to 375 °F/190 °C and continue cooking for about 1 hour and 10 minutes, occasionally basting the meat.
Remove the lid, add the maple syrup and port for the last 15 minutes of cooking, raising the heat to 400 °F/200 °C.
Remove the meat, cover it and let sit for 15 minutes.
Reduce the cooking liquid by half and add the cream and cornstarch if needed.
Chef’s Tip
Take the lamb out of the refrigerator one hour before cooking to allow it to come to room temperature, for a tender and delicious meat.