Preheat Sous Vide to 55 degrees celsius in a large tub of water. Pack the rack of lamb dry and season generously on both sides with salt and pepper. Toss lamb into ziploc bag with rosemary and garlic. Vacuum seal the bag as best you can and place in water. Sous vide for 2 hours.

In food processor, combine parsley, mint, garlic, and lemon juice. While the machine is on, add olive oil in a steady stream until pesto thickens. Add salt to taste.

After 2 hours, take lamb out of bag and sear in hot pan with the fat cap down. Sear for a minute on each side. Let rest for a few minutes before cutting and serving.