Ingredients: 1 tablespoon vegetable oil2 onions, peeled and chopped450g minced beef1 tablespoon plain flour450ml beef stock1 tablespoon Worcestershire sauce1 tablespoon tomato pureeSea Salt and freshly ground black pepper900g potatoes, peeled and cut into chunks25g butterAbout 4 tablespoons milkMethod: Heat the oven to 170°C/Fan 150°C/gas mark 3 ½Heat the oil in a casserole dish and fry the onions over a low heat for 5 minutes. Increase the heat to medium, add the beef and cook until it just browns.Stir in the flour, stock, Worcestershire sauce and tomato puree. Bring the mixture to the boil and season, then cover with a lid, transfer to the oven and bake for 20 minutes.Meanwhile, boil the potatoes in salted water until tender. Drain them and return them to the pan. Mash the potatoes with butter and a splash of milk but don't overdo it - sloppy mash is unforgivable.Remove the casserole from the oven, then increase the oven temperature to 220°C/fan 200°C/gas mark 7.Spoon the beef mixture into a medium pie dish and spread the mashed potato over the top.Bake for 25 minutes until the potato starts to brown. (If you like, add a sprinkling of grated cheese just before you're due to take it out of the oven and return the dish to the oven until the cheese is melted and bubbling)Serve immediately.