Preheat the oven to 425 F (220 C). Rub the lamb with the olive oil, salt and pepper.
In an oven-safe dish, cover the bottom with the garlic and onions and place the lamb over top. Cook for 30 minutes.
Reduce the temperature to 320 F (160 C). Mix the wine and tomato sauce and pour into the dish. Add the rosemary and bay leaves. Cover with aluminum foil and cook for 3.5 to 4 hours.
Once tender, remove the lamb and keep it warm.
In a sauce pan, bring the cooking liquid to a boil with the butter. Reduce by half, stirring constantly.
Chef’s Tip
This recipe can be made with a Quebec leg of lamb.