Dry fry the lamb with the onion, bay leaf, mushrooms and carrot for 8-10 minutes.
Add the flour and cook, stirring, for 1 minute. Gradually add the stock and tomato puree. Cook, stirring, until the mixture thickens and boils.
Cover and simmer gently for 25 minutes. Remove the bay leaf and season to taste. Spoon into a 1.7 litre (3 pint) oven proof dish.
Meanwhile, cook the potatoes in boiling salted water for 20 minutes until tender. Drain well. Mash with the butter and milk and mix well. Pile on to the mince mixture and sprinkle over the cheese.
