Preheat the oven to 325˚F. Heat a large sauté pan with high sides until very hot. Salt and pepper the lamb shanks heavily. Add olive oil to the pan and add the lamb and sear hard on each side until golden brown. Remove from the pan and set aside at room temperature.
Add the vegetables and garlic to the sauté pan and cook until browned. Add the tomato paste and cook for an additional four minutes, stirring constantly. Deglaze the vegetables with the red wine, making sure to scrape all the brown caramelization from the bottom of the pan.
Put the lamb back in the sauté pan and add the thyme and bay leaf. Cover with veal stock, about an inch above the lamb, squeeze the oranges into the pan, and add the halves. Cover tightly and cook in the oven for about two hours (depending on the size of the lamb shanks) until very tender.
When done, remove lamb and strain the braising liquid. Put it in a pan and reduce until thick. Finish with the Gran Gala and butter. Salt and pepper to taste. Serve with roasted root vegetables and sugar snap peas.