Place the beef into a 5-quart slow cooker. Add the brown sugar, garlic, thyme and flour and toss to coat.
Stir the soup and ale in a small bowl. Pour over the beef.
Cover and cook on LOW for 8 to 9 hours* or until the beef is fork-tender. Serve with the mashed potatoes.
*Or on HIGH for 4 to 5 hours.