Season the short ribs generously with salt and pepper. In a large heavy skillet or roasting pan, heat the olive oil to med-high. Begin searing each of the short ribs on all sides, turning the heat to high if necessary for browning. When searing is complete, remove ribs from pan and set aside. Place onion and garlic in hot pan and saute for 2-3 min. Add red wine, reduce by ½. Add stock and reduce by 1/4. Add tomato puree, chili flakes and rosemary, place ribs back in pan, cover and simmer over low heat for 2-3 hrs or until ribs are fall-off-bone tender. Can also be done in oven, covered at 300 degrees. When ribs are done, baste well with sauce, garnish with pancetta and serve with sauce.