Prep the Marinade: In a small bowl, combine the minced garlic, rosemary, thyme and olive oil. Mix well.
Prepare the Lamb: Pat the bone-in leg of lamb (4–5 lbs) dry with paper towels. Trim off any excess fat if needed, but leave a thin layer for flavor and moisture.
Marinate: Rub the herb oil generously over the entire surface of the lamb, season generously with salt and pepper making sure to get into any crevices. Cover the lamb with plastic wrap and refrigerate for at least 4 hours, or ideally overnight for maximum flavor.
Bring to Room Temp: Remove the lamb from the refrigerator about 1 hour before roasting to bring it to room temperature. Preheat the oven to 450°F (232°C).
Sear the Lamb: Place the lamb on a rack in a roasting pan. Roast at 450°F for 15–20 minutes to develop a golden crust.
Roast Low and Slow: Reduce the oven temperature to 325°F (163°C) and continue roasting until the internal temperature reaches:125°F for rare130–135°F for medium-rare140–145°F for mediumThis usually takes about 20–25 minutes per pound. Rest: Remove the lamb from the oven and tent loosely with foil. Let it rest for 15–20 minutes before carving. This helps the juices redistribute and keeps the meat tender.
