03Add the stock, carrots, celery, onions and tomato paste to the pan. Tightly cover the pan with foil, and cook in the oven for 4 hours.04Remove the pan from the oven, then check the tenderness of the meat, it should be fork tender. If need be, continue cooking to achieve desired tenderness. Then remove the ribs and save the remaining liquid. Over medium-high heat reduce the braising liquid until the liquid has reduced to 2 cups.05Serve the osso bucco with mashed potatoes, then drizzle with sauce and finish with feta crumble.