Trim the meat of any fat or gristle, and cut into 2-inch cubes. Toss beef with 1 tablespoon of the oil. In a small bowl, season the flour with salt, pepper and cayenne. Toss meat with seasoned flour. Heat remaining 2 tablespoons oil in a large skillet over high heat. Brown the meat on all sides. Reduce the heat, add the onions, crushed garlic and tomato puree to the skillet, cover, and cook gently for 5 minutes. Transfer the contents of the skillet to a casserole and pour half of the Guinness into the skillet. Bring Guinness to a boil and stir to dissolve the caramelized meat juices on the pan. Pour over the meat, along with the remaining Guinness. Add the carrots and thyme. Stir and adjust seasonings. Cover the casserole and simmer over low heat, or in a 300 degree F oven until the meat is tender, 2 to 3 hours. Garnish the beef with parsley and serve.