1. Preheat the oven to 180°C/350°F/Gas Mark 4.
2. Heat the butter and oil in a large ovenproof pan over a medium heat until the butter has melted and begins to foam.
3. Add the beef and brown on all sides (you may need to do this in batches). Remove the beef from the pan and leave to one side. In the same pan, add the sliced onions and cook slowly until they begin to soften. Continue to cook until the onions are caramelised and golden brown, this will take around 15 minutes.
4. Return the beef to the pan and along with any juices. Add the flour, stir and cook for two minutes. Add the thyme, bay leaves, beer and stock to the pan ensuring the meat is covered in the liquid.
5. Scrape the browned bits from the bottom. Add the mustard coated bread. Cover with a lid and place in the oven to cook for two hours, or until the meat is tender.
6. Heat your oven to 200°C/Gas Mark 6. Peel the potatoes and cut into chips, wash and pat dry.
7. Coat the potato chips in the melted butter. Divide the stew into individual ovenproof bowls, top with the potato chips to form a layer over the surface of the stew.
8. Season with a little salt then bake for 30-40 minutes until the chips are cooked and golden brown.
9. Remove from the oven leave to stand for 5 minutes before serving.