Season the flour with salt and pepper, and use to coat the beef. Melt the butter with the oil in a large frying pan on the hob. Fry the beef, in batches, until browned. Transfer to a casserole dish. Add the onion, carrots and celery to the frying pan and fry gently for a further 5 minutes. Add to the casserole dish.
Pour the ale and stock into the frying pan and add the tomato purée, sugar, mustard and a little salt and pepper. Bring just to the boil and pour into the casserole dish. Cover with foil and place on the lower rack of the halogen oven.
Set the temperature to 200°C (392°F) and cook for about 50 minutes until the meat is tender. Check the seasoning before serving. Serve with a root mash.