Method
1. Trim, peel and finely chop the onion. Trim, peel and dice the carrots. Halve or quarter the mushrooms. If small, leave them whole. Pick the thyme leaves off their woody sprigs.
2. Place a large, heavy-based pan or casserole dish on a high heat. Add 1 tbsp oil and half the stewing steak. Season with salt and pepper. Fry for 3-4 mins, turning once or twice, till browned. Scoop out of the pan into a bowl. Add another 1 tbsp oil to the pan, then repeat with the remaining stewing steak.
3. Turn the heat down to medium-low. Add the onion, carrots, mushrooms and thyme to the pan. Add 4 tbsp water. Season with salt and pepper. Fry for 10-12 mins, stirring often, till softened.
4. Fill and boil your kettle. Crumble the vegetable stock cube into a heatproof jug. Pour in 400ml hot water. Stir to dissolve.
5. Return the beef and its juices to the pan. Stir in the cornflour and cook for 1 min. Gradually stir in the stock. Bring the mixture to the boil. Turn the heat down to low. Pop a lid on the pan. Simmer for 1½ hrs, stirring occasionally, till the beef is tender. If the mixture seems too dry, add a splash more water.
6. Preheat your oven to 180°C/Fan 160°C/Gas 4. Dust your work surface with flour. Unwrap the pastry and roll it into a large, thin piece the same shape as your pie dish, approximately ½cm thick. No flour? You can roll the pastry out between 2 sheets of baking paper.
7. Spoon the mixture into a 1 ltr pie or baking dish. Lay the pastry over the top, lightly crimping it to the edges of your dish with a fork. If you have any excess pastry, you can cut shapes to decorate your pie. Brush the top of the pastry with a splash of milk or beaten egg, if liked.
8. Using a sharp knife, cut a small hole in the centre of the pastry to help any steam escape (this will help the pastry cook evenly). Place the pie onto a baking tray and slide into the oven. Bake for 25 mins till the pastry is golden and crisp. Serve straight with your favourite vegetable sides.
9. Get Ahead
You can make the pie filling the day before, then let it cool and store it in the fridge. The pie filling is also great made in a slow cooker. Let it cook on low for 6-8 hrs, then top with the pastry and bake in the oven.