Heat oven to 400 degrees F. Season the lamb shanks with salt, pepper thyme and rosemary. In a heavy metal roasting pan, brown the lamb shanks over medium heat in olive oil on stovetop. When shanks are half browned, add the onion, carrot, celery, potato, and garlic. Caramelize all the vegetables while stirring often until golden brown. Strain the fat from the vegetables and shanks. Dust pan with flour and cook it until everything is well coated in the flour. Add the chicken stock, white wine, and port wine. Place the pan, uncovered, in the oven for 2 hours.

When shanks are cooked, remove them from the sauce. They should be tender, but not falling off bone. Puree the vegetables and sauce together and strain through a fine sieve. Taste for seasoning, and add balsamic vinegar..

Serve the lamb shanks with the sauce. Mashed potatoes and Brussel sprouts make a nice accompaniment to this dish.