1 tbsp. oil
1 onion, peeled and chopped
450 g. (1 lb.) minced beef
1 x 225 g. (8 oz.) can tomatoes
1 tbsp. tomato puree
1 tsp. dried thyme
1/2 tsp. mustard powder
Salt and freshly ground black pepper
1 tbsp. corn flour
2 tbsp. water
25 g. (1 oz.) butter
225 g. (8 oz.) button mushrooms, sliced
1 tbsp. chopped fresh parsley
350 g. (12 oz.) cooked potato, mashed and seasoned
15 g. (1/2 oz.) cheddar cheese, grated

Heat the oil in a large pan. Add the onion and fry gently until light golden. Stir in the minced beef and continue cooking until the meat is lightly browned. Stir in the tomatoes and their juice, tomato puree, thyme, mustard powder, salt and pepper, then bring to the boil. Cover and simmer for 25 minutes, stirring occasionally.

Mix the corn flour with the water and stir into the mixture. Simmer for a further 3-4 minutes, then remove from the heat and set aside. Melt the butter in a small pan; add the mushrooms and fry gently for 2-3 minutes. Stir in the parsley, then allow them to cool.

Spoon half the meat mixture into a 1.2 liter (2 pint) pie dish or foil container, then cover with the mushroom mixture. Spoon over the remaining meat mixture, then top the pie with the mashed potato. Smooth the surface of the potato, then make a pattern on the top with a fork.

Sprinkle the pie with grated cheese. Bake in a preheated oven at 160 degrees C (325 degrees F) for 35-40 minutes. Put under a preheated hot grill to brown the top of the pie. Serve immediately.