Leg of Lamb

Prepare the leg of lamb the day before. Mix 3 tablespoons of olive oil and mustard in a bowl, then add the chopped thyme leaves and crushed garlic cloves. Rub this mixture over the leg of lamb and wrap in cling film. Refrigerate for 24 hours to let the flavors penetrate the meat.

The next day, prepare the gratin. Preheat the oven to 150°C. Peel the potatoes, cut into 1.5 cm thick slices, and place in a baking dish. In a bowl, mix the cream and milk, then add the crushed garlic. Season with salt and pepper. Pour over the potatoes, cover the dish with aluminum foil, and bake for 1 hour and 40 minutes. Remove the foil, sprinkle the grated cheese over the potatoes, and bake in the oven for 30 minutes. Keep warm.

Set the oven to 160°C. Sear the leg of lamb in the remaining olive oil in a pan, place in a roasting pan, and roast for 40 minutes (if using a meat thermometer, it should read 48°C in the center). Turn off the oven, wrap the lamb in aluminum foil, and let it rest in the oven with the door open to tenderize the meat.

Deglaze the roasting pan with white wine to loosen all the cooking residues from the bottom of the pan, then stir in the broth, water, and mustard. Strain this gravy through a fine mesh sieve into a small pot and stir in the butter over low heat. Carve the leg of lamb into thick slices and arrange on hot plates. Drizzle with the gravy and serve with the gratin.