Heat the oil in a large, heavy-bottomed braising pan over medium-high heat. Season the beef shanks with salt and pepper. Sear the beef shanks, cooking for about 7 minutes on each side until a dark brown crust forms. Remove them from the pan and set aside.
Add in the shallots to the pan. Cook for 5 minutes, until softened. Add in the flour and continue to cook another 3-4 minutes, until the flour is golden brown.
Add the beef shanks back to the pot along with the rosemary sprigs. Pour the Guinness over them. Cover the braiser and move the pan to the oven.
Braise in the oven for 3 hours.
Remove from the oven. Uncover and pull the beef shanks from the sauce. Pull apart slightly on a plate.
Skim any excess grease from the top of the sauce remaining in the pan. Cook the sauce over medium-high heat for 4 minutes or until thickened slightly. Add the meat back in pan and serve over polenta along with the bones, if desired. Sprinkle with blue cheese.