Preheat your oven to 150˚C (fan-forced).

Poke holes all over the lamb leg with a small knife, then insert garlic cloves into the holes.

Drizzle beef tallow over the lamb and sprinkle the seasoning on it.

Place the lamb on a rack in a roasting pan.

Carefully pour red wine, beef stock, and Dijon mustard on the sides, avoiding the lamb leg. Pour about 2-3 cups of water to fill the roasting pan beneath the leg – do not submerge the lamb.

Cover the roasting pan with foil and put it in the oven for 5 hours. Turn the lamb over when it feels tender, then return it to the oven for 1 hour. Thereafter rest the lamb for at least 30 minutes, loosely covered with foil.

Take the juices from the roasting pan and make a roux with 3 tablespoons of flour in a saucepan over medium heat. Continuously whisk the mixture while adding a small amount of water at a time. Once you are satisfied with the consistency, season the gravy with salt and pepper.