A few hours before you want to begin roasting, set the lamb out on the counter to come to room temperature.
Adjust the oven rack to the lower-middle position of the oven. Preheat to 275 F.
Line a roasting pan with foil and place a rack in it.
Remove lamb from packaging and pat dry with paper towels. Rub the salt and pepper into the outside of the meat.
Place the lamb unto the rack and roast in the preheated oven and roast until the desired temperature is reached with an instant read thermometer inserted into the coolest section of the lamb:
F – 130 F for medium-rare (The lamb I cooked for the photos was pulled at 130 F)
F – 135 F for medium
This takes about 2 to 2 ½ hours depending on your oven and the weight of the meat.
When desired temperature is reached, remove the lamb from the oven and let it rest for 40 minutes while you prepare any side dishes you want to serve.
Increase the oven temperature to 500 F and return the lamb to the oven after resting. Roast until the outside is dark brown and crispy, about 15 minutes. Remove from the oven and let rest another 5 minutes.
Remove twine with kitchen shears and transfer the lamb to a cutting board. Slice into ¼” slices and serve.