Lower the oven rack to below center and preheat oven to 325℉
Add the stock to the roasting pan and place rack in pan.
Remove plastic wrap from lamb (over sink) and pat lamb dry.
Lay lamb leg on the rack in pan.
Score any large areas of fat on the leg of lamb.
In a small bowl add the diced garlic, Dijon and oil, mix well.
Using your basting brush slather the lamb with the Dijon coating.
Cover the lamb in the roasting pan and put in the preheated oven.
Slow roast for three hours for well-done / two hours for rare.
Wash, peel, and cut root vegetables.
Remove lamb from oven and add the root vegetables around the base of the meat.
Cover and return to oven for an additional hour.
Remove from oven and test vegetables for done. They should have soaked up moisture from the meat and started to caramelize.
Remove the roast from the oven and put on serving tray to serve.
Serve while hot.