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Lamb Sirloin Roast

  • Author: Maxine Dubois
  • Total Time: 1 hour 40 minutes
  • Yield: 6-8 servings 1x


This Lamb Sirloin Roast is made with bone-in roasted leg of lamb flavored with garlic, olive oil, fresh rosemary, lemon juice and red wine. 


  • 4 to 5 trimmed bone-in leg of lamb
  • 4 cloves garlic, crushed into a paste
  • 3 tablespoons olive oil
  • 1 tablespoon chopped fresh rosemary
  •  1 tablespoon lemon juice
  • 1/3 cup red wine
  • 1 tablespoon kosher salt
  • 2 teaspoons ground black pepper


  1. Preheat the oven to 325°F (165°C).
  2. In a small bowl, mix together the crushed garlic, olive oil, chopped rosemary, lemon juice, red wine, kosher salt, and black pepper to create a marinade.
  3. Place the trimmed bone-in leg of lamb in a roasting pan or baking dish. Make several small cuts or slits in the lamb to allow the marinade to penetrate the meat.
  4. Pour the marinade over the lamb, making sure to coat it evenly. Use your hands or a brush to massage the marinade into the lamb, ensuring it is well-covered.
  5. Cover the roasting pan or baking dish with aluminum foil and let the lamb marinate in the refrigerator for at least 2 hours, or overnight for even better flavor.
  6. Once marinated, remove the lamb from the refrigerator and let it sit at room temperature for about 30 minutes before cooking.
  7. Remove the foil and place the lamb in the preheated oven. Roast for approximately 20 minutes per pound of lamb, or until the internal temperature reaches your desired level of doneness. In this case, I roasted for an hour and 20 minutes. The recommended internal temperature for medium-rare lamb is 135°F (57°C).
  8. Halfway through the cooking time, baste the lamb with the juices from the roasting pan to keep it moist and flavorful.
  9. Once cooked to your liking, remove the lamb from the oven and cover it loosely with foil. Allow it to rest for about 15 minutes before carving. This helps the juices redistribute within the meat for a more tender and flavorful roast.
  10. Slice the lamb into thin or thick slices, depending on your preference, and serve with the pan juices as a flavorful sauce.


  • Bring the lamb to room temperature: Before roasting, allow the lamb to sit at room temperature for about 30 minutes to an hour. This helps promote more even cooking and ensures the lamb cooks more consistently throughout.
  • Season the lamb generously: Season the lamb sirloin roast generously with salt and pepper, or your preferred seasoning blend. Don't be afraid to coat the meat thoroughly, as this enhances the flavor of the lamb.
  • Use a meat thermometer: To achieve the desired level of doneness, it's highly recommended to use a meat thermometer. Insert it into the thickest part of the lamb, away from the bone, to ensure accurate readings. The internal temperature should be around 135°F (57°C) for medium-rare, 145°F (63°C) for medium, or adjust according to your preference.
  • Let it rest: After removing the lamb from the oven, let it rest for about 10 to 15 minutes before carving. This allows the juices to redistribute within the meat, resulting in a more tender and juicy roast.
  • Carve against the grain: When it's time to carve the lamb, remember to cut against the grain. This helps ensure each slice is tender and easier to chew.
  • Make use of pan drippings: While the lamb rests, you can make a delicious sauce using the pan drippings. Skim off excess fat, then deglaze the pan with some wine or broth. Simmer and reduce the liquid until it thickens slightly. Strain the sauce, adjust the seasoning if needed, and serve it alongside the lamb.
  • Pair with complementary flavors: Consider serving the lamb sirloin roast with complementary flavors such as mint sauce or jelly, roasted vegetables, garlic mashed potatoes, or a side of fresh salad. These accompaniments can enhance the overall dining experience and balance the richness of the lamb.
  • Slice it right: To achieve consistent and appealing slices, use a sharp carving knife and a carving fork. Slice the lamb against the grain into thin or thick slices, depending on personal preference.
  • Prep Time: 10 minutes
  • Cook Time: 1 Hour 30 minutes
  • Category: Dinner
  • Method: Baking
  • Cuisine: American


  • Serving Size: 1
  • Calories: 126.9
  • Sugar: 0.0 g
  • Sodium: 15.5 mg
  • Fat: 9.3 g
  • Saturated Fat: 2.0 g
  • Carbohydrates: 5.1 g
  • Fiber: 2.7 g
  • Protein: 8.1 g
  • Cholesterol: 27.3 mg