For best results, let the lamb come to room temperature for 30 minutes before roasting.
The internal temperature will rise about 5°F during the resting period. For well-done, roast until the thermometer reads 160°F.
Mint sauce can be made up to 24 hours in advance. Store covered in the refrigerator and bring to room temperature before serving.
If fresh rosemary is unavailable, use 1 teaspoon of dried rosemary, though fresh is preferred for better flavor.