Preheat a sous vide immersion circulator to desired final temperature according to chart above and in notes section. Season lamb generously with salt and pepper. Place racks in two individual sous vide bags, along with herbs, garlic, and shallots , and distribute evenly. Seal bags using a vacuum sealer, or seal plastic zipper-lock bags using the water displacement method . Place bags in preheated water bath for desired time according to chart above.