In a heavy based saucepan, heat the oil. Dust the ribs lightly in the flour, shaking off any excess flour. Seal the ribs on all sides, remove and place on a plate. Do this in batches so not to crowd the pan. Turn down the heat and add the onions, celery, garlic, thyme and bay leaves and sweat until softened but not colored. Deglaze the saucepan with a little of the Guinness® Foreign Extra Stout and add the browned ribs back into the pan. Add the remaining Guinness and beef stock and season to taste with the salt and pepper. Bring to a boil and cover and cook over a low heat for 3 hours. Once the ribs are cooked and the meat is falling off the bone, carefully remove the ribs with a slotted spoon and place in a serving dish. Turn the heat up on the saucepan and reduce the sauce until you have about a pint of liquid remaining. Pour the sauce over the ribs and serve.