Toss beef with flour, salt and pepper. Heat oil in a heavy pan over high. Brown beef in batches, 3 minutes per side. Tip into the slow cooker.
Same pan, cook onions 5 minutes. Add garlic 30 seconds. Tip into cooker.
Add wine to the pan. Boil 2 minutes scraping the bottom. Pour into cooker.
Add carrots, potatoes, stock, tomato paste, mustard, thyme and bay to the cooker. Stir.
Cover. Cook on low 8 hours (or high 4-5 hours).
Taste. Adjust salt and pepper. Discard bay and thyme stems. Serve in deep bowls.