Remove the mutton from the fridge and bring to room temperature. Like so many meats, they are better when not transferred from cold environment to a hot one quickly. Pat dry to remove any moisture.
Pre heat your oven to 200 Celsius
Season the leg of Mutton well with salt and pepper and a drizzle of olive oil.
Use a large heady duty roasting tray with high sides and handles. This makes it easier to mov the pan in and out of the oven.
Chop the carrots, onion and celery to make a mirepoix for the leg to lay on. Add a bay leaf, few sprigs of rosemary and a few garlic cloves. These should be placed in the base of the tray with the mutton on top.
Locate the joint skin side up onto the chopped veg.
Place the tray in the centre of your oven and roast for 20 minutes.
After 20 minutes, reduce to 190 Celsius an continue to roast for 30 minutes per 500g.
The temperature at the thickest part of the leg needs to reach at least 65 Celsius.
One cooked, remove from the oven and place the leg on a clean dish and cover with foil to allow it to relax.
The vegetables in the pan can be used as part of the gravy.