In a small bowl, mix the minced garlic, chopped rosemary, olive oil, salt, black pepper, lemon zest, and lemon juice. Add the Dijon mustard and mix well.
Place the lamb leg in a large resealable plastic bag or a shallow dish.
Pour the marinade over the lamb, making sure it's evenly coated.
Seal the bag or cover the dish with plastic wrap and refrigerate for at least 2 hours or overnight for best results. Allow the lamb to come to room temperature before roasting.
Preheat your oven to 180°C (350°F).
Place the marinated lamb leg on a roasting rack set inside a roasting pan. If you don't have a rack, you can place it directly in the pan.
Pour the chicken or vegetable broth and white wine (if using) into the bottom of the roasting pan.
Roast the lamb in the preheated oven for approximately 20 minutes per 500 grams of meat. For a 1.5 kg lamb leg, this would be around 60 minutes. Use a meat thermometer to ensure your lamb reaches your desired doneness. For medium-rare, aim for an internal temperature of 55-60°C (130-140°F). For medium, aim for 63-68°C (145-155°F).
Once the lamb reaches your desired temperature, remove it from the oven and let it rest for about 15 minutes. Tent it loosely with aluminum foil to keep it warm.
Carve the roasted lamb leg into thin slices and serve with your favorite sides, such as roasted vegetables, mashed potatoes, or a fresh salad.Enjoy your delicious roasted lamb leg with this metric recipe!