Heat the oil in a large frypan over medium heat. Toss beef cubes with flour to coat then fry in the hot oil until browned. Place the carrots, potatoes, onion and garlic in a large slow cooker. Place the meat on top of the vegetables. Mix together the beef stock and tomato paste and pour into the slow cooker along with the beer.
Cover and cook on High for 6 hours or Low for 8 hours. During the last hour before serving dissolve the cornflour in cold water and then stir into the broth. Simmer on the High setting for a few minutes to thicken.