In a deep pot, heat the oil until it is hot but not smoking. Sear the shanks until each side is dark brown. Remove shank from pot.
Lower the heat to medium, and add the onions. Let the onions cook for 5 minutes, or until the begin turning translucent.
Add the carrots and the garlic, and let cook for another 5 minutes. If the ingredients are beginning to stick to the pot, add a splash of red wine to loosen them up. Add the tomato paste and rosemary leaves. Mix everything so that the vegetables are fully coated. Sauté for another 5 minutes to let the flavors meld.
Place the shanks back into the pot. Pour the remaining wine and water into the pot. Bring the mixture to a boil, and then turn dow the heat to a low-medium heat, or until the liquid hits a low simmer. Place the lit on the pot and let cook for 4-5 hours, or until the meat is fork tender.
Once tender, remove the meat from liquid. Strain and discard the vegetables. Return the steak back into the pot with the liquid, and reduce the liquid by half. Season to taste with salt and pepper.