Step 1: Butterfly the Leg of Lamb (If Not Already Butterflied)

• Position the Lamb: Place the leg of lamb on a cutting board, fat-side down, with the shank bone facing away from you.
• Make the First Cut: Starting at the thickest part of the lamb, make a deep lengthwise cut along one side of the bone, cutting almost to the bone but not through it.
• Continue Butterflying: Open the lamb like a book, and continue to butterfly it by spiraling your knife around the bone, opening it up as you go, and maintaining an even thickness. The goal is to create a relatively even, flat piece of meat that can be stuffed and rolled.
• Trim Excess Fat (Optional): Trim away any excess thick pieces of fat from the inside of the butterflied lamb. A thin layer of fat is desirable for flavor and moisture, but very thick pieces can be removed.

Step 2: Marinate the Butterflied Lamb

• Prepare Marinade: In a small bowl, whisk together the olive oil, lemon juice, minced garlic, chopped rosemary, chopped thyme, salt, and black pepper.
• Marinate Lamb: Place the butterflied leg of lamb in a large resealable plastic bag or a shallow dish. Pour the marinade over the lamb, ensuring it is evenly coated.
• Marinate in Refrigerator: Seal the bag or cover the dish and marinate the lamb in the refrigerator for at least 2 hours, or ideally overnight, for maximum flavor penetration and tenderization.

Step 3: Prepare the Savory Stuffing

• Sauté Sausage: In a large skillet, heat olive oil over medium heat. Add the Italian sausage (casings removed) and cook, breaking it up with a spoon, until browned and cooked through. Drain off any excess grease.
• Sauté Vegetables: Add the diced onion and celery to the skillet with the sausage. Sauté, stirring occasionally, for about 5-7 minutes, or until the vegetables soften.
• Add Mushrooms and Garlic: Add the sliced cremini mushrooms and minced garlic to the skillet. Sauté for another 5-7 minutes, or until the mushrooms are softened and browned and the garlic is fragrant.
• Combine Stuffing Ingredients: In a large bowl, combine the sautéed sausage and vegetable mixture, breadcrumbs, chicken broth (or white wine), chopped parsley, chopped mint, dried sage, salt, and black pepper. Mix well to combine all ingredients evenly.
• Taste and Adjust Seasoning: Taste the stuffing and adjust seasoning as needed. You may want to add more salt, pepper, sage, or herbs to your preference.

Step 4: Stuff and Tie the Leg of Lamb

• Preheat Oven: Preheat oven to 350°F (175°C).
• Spread Stuffing: Remove the marinated leg of lamb from the refrigerator and lay it flat on a cutting board, with the inside facing up. Spread the prepared stuffing evenly over the surface of the butterflied lamb, leaving a small border around the edges.
• Roll and Tie: Starting from one of the shorter ends, roll up the lamb tightly like a jelly roll, enclosing the stuffing inside. Use kitchen twine to tie the lamb roast securely at several intervals (about every 2-3 inches) to hold its shape during roasting. Also tie twine around the roast lengthwise in a few places for added security.

Step 5: Roast the Stuffed Leg of Lamb

• Sear (Optional for extra browning): For extra browning and flavor, you can sear the stuffed and tied leg of lamb before roasting. Heat a tablespoon of olive oil in a large oven-safe skillet or roasting pan over medium-high heat. Sear the lamb roast on all sides until browned, about 2-3 minutes per side. This step is optional but enhances the color and flavor of the roast.
• Roast in Oven: Place the seared (or unseared) stuffed leg of lamb in the roasting pan. Roast in the preheated oven for approximately 1 hour and 15 minutes to 1 hour and 45 minutes, or until a meat thermometer inserted into the thickest part of the lamb (not touching the stuffing) registers 135°F for medium-rare, 145°F for medium, or 150°F for medium-well. Roasting time will vary depending on the size and thickness of the lamb and your desired level of doneness.
• Rest the Lamb: Once the lamb reaches your desired temperature, remove it from the oven and transfer it to a cutting board. Tent it loosely with foil and let it rest for at least 15-20 minutes before carving. Resting allows the juices to redistribute throughout the lamb, resulting in a more tender and flavorful roast. The internal temperature will continue to rise slightly during resting.

Step 6: Make the Mint Yogurt Sauce (While Lamb Rests)

• Combine Sauce Ingredients: While the lamb is roasting and resting, prepare the mint yogurt sauce. In a food processor or blender, combine the Greek yogurt, packed fresh mint leaves, minced garlic, lemon juice, and salt.
• Blend Until Smooth: Blend until the sauce is smooth and creamy, scraping down the sides of the bowl as needed. Taste and adjust seasoning, adding more salt or lemon juice to your preference.
• Chill (Optional): For a colder sauce, chill the mint yogurt sauce in the refrigerator until ready to serve. The sauce can also be served at room temperature.

Step 7: Carve and Serve

• Remove Twine: Before carving, carefully remove the kitchen twine from the roasted leg of lamb.
• Carve and Serve: Carve the stuffed leg of lamb into slices, about ¾ inch thick, and arrange them on a serving platter.
• Drizzle with Mint Yogurt Sauce: Generously drizzle the carved lamb slices with the refreshing mint yogurt sauce.
• Garnish (Optional): Garnish the platter with fresh mint sprigs or lemon wedges for visual appeal.
• Serve Immediately: Serve the Stuffed Leg of Lamb with Mint Yogurt Sauce immediately while it is warm and juicy.