Dry of the lamb shanks with paper towel. This will help with browning. Heat half of the grape seed oil in a large pot over medium to high heat. Season the lamb shanks with cracked black pepper and sea salt, brown on all sides. Once golden brown remove the lamb from the pot and set aside. Add in the remaining grape seed oil along with the onions, garlic and leeks. Brown for a minute and then add in the chopped peaches, tomatoes, rosemary and cardamom. Continue to brown for another minute and then add in the peach cider. Simmer for a few minutes to reduce the liquid by half and then add in the beef stock and the seared lamb shanks. Once the stock comes up to a simmer, cover and place in a 400 degree oven for approximately 45 to 50 minutes, until the meat pulls from the bone. When you are ready to serve remove the cooked lamb shank from the pot. Strain of the braising liquid, season and serve.