When roasting a rack of lamb that weighs between 1 1/2 and 2 1/2 pounds, the ideal cooking time at 375 degrees Fahrenheit ranges between 30 and 40 minutes, depending on how thoroughly the lamb should be cooked. Medium-rare racks come out after 30 minutes, whereas well-done racks cook for 40 minutes.
Before roasting a rack of lamb, the best way to get vivid flavors is to use a marinade to treat the meat overnight. Combining spices, such as rosemary and thyme, with garlic and olive oil creates a coating that brushes right onto the rack. Rubbing this marinade into the lamb and wrapping the racks in plastic wrap for overnight storage in the refrigerator allows the flavors to seep into the meat.
While cooking times are a good way to determine the progress of the lamb in the oven, a meat thermometer delivers the final verdict. For a medium-rare rack of lamb, the thermometer should read 145 degrees Fahrenheit. However, lambs cooked to medium should be cooked until the thermometer hits 160, and for a well-done rack of lamb the correct temperature is 170 degrees. Because the lamb continues to cook after removal from the oven, removing the rack when the temperature is 5 or 10 degrees below the desired level cooks the lamb correctly without drying out the meat.