Toss the beef in seasoned flour. Brown in batches in hot oil in a large casserole. Set aside.
Cook the onion, carrot and celery for 8-10 minutes, add garlic and tomato purée, cook 1 minute more. Return the beef, add stock, stout, bay leaves and Worcestershire sauce. Bring to a simmer.
Cover and cook low and slow at 150°C (130°C fan) for 2.5-3 hours until the beef is fork-tender.
Cool the filling completely. Transfer to a pie dish, top with puff pastry, trim and crimp, brush with egg, cut a vent. Bake at 200°C (180°C fan) for 25-30 minutes until risen and golden.