1. Add garlic, mint, rosemary, and salt to a food processor. Pulse until chunky. Add oil through the feeder tube, and continue to process until mixture is pureed.
2. Place lamb on a cutting board. Roll it out, fat-side down, into one flat piece and cut off any gristle. Spread mint mixture over the surface of the lamb. Roll up the lamb lengthwise and use butcher's twine to tie it every 1 to 2 inches to hold it together. Place in a resealable plastic bag and refrigerate for at least 2 hours and up to 24 hours.
3. Remove from fridge 30 minutes prior to cooking. Preheat oven to 450 degrees F. Season lamb with pepper and place in a roasting pan. Cook 20 minutes, then lower heat to 325 degrees F and cook until an instant-read thermometer reads 135 degrees F for medium-rare, about 50 to 70 minutes. (Check a couple areas of the lamb to make sure they register the same temperature.)
4. Remove lamb from oven and let rest 15 minutes. Place on a cutting board, cut twine off the lamb, and cut lamb into 1/4-inch slices. Place slices on a serving platter, garnished with sprigs of mint and lemon slices if desired.
Source: Hannaford fresh Magazine, March - April 2014