Delicate pork tenderloin is the extra-lean meat adjacent to the loin. This tasty, supple little muscle has a tendency to dry out quickly during cooking and can go from perfectly pink to dry and mealy the second you turn your back on the saute pan. Our solution is to provide the tenderloin with a protective layer of much-needed fat in the form of rich, salty pancetta. As the tenderloin roasts, the pancetta crisps, basting the lean muscle with its fat so that it remains moist and infusing it with its robust flavor. Roasted radicchio is an excellent accompaniment.