This recipe for braised lamb shanks can easily be done in the oven, but with the Instant Pot you can cut out at least an hour of the cook time. The basic method for cooking lamb shanks in the Instant Pot: 60 minutes on high pressure, 15 minutes natural release then quick release any remaining pressure. To cook lamb shanks in the oven, you'll want to first brown the shanks then braise them covered in a 300-degree oven for 1½. Remove the lid and braise for another hour, rotating the shanks occasionally.