1. Heat the oil in a large stock pot and cook the onion and carrot with a sprinkling of salt for a few minutes until tender. Remove from the pot and keep to one side.
2. Turn up the heat slightly. Season the steak with salt and pepper and cook in batches so it is evenly browned all over. Don’t be afraid of some bits going almost burnt on the edges. Remove from the pot and keep to one side.
3. Melt the butter in the pot and fry the mushrooms with the fresh thyme for 2 minutes. Put the onion, carrot and steak back in the pan then stir in the flour. Pour in the stock and bring to the boil. Gently simmer on the lowest heat with a lid on for 2 hours. The sauce should gradually thicken and the steak will tenderise. Add further seasoning when nearly ready if required.
4. Just before the filling is ready, heat your oven to 180C/Gas Mark 4. Roll out your puff pastry onto a floured surface until you have enough to cover your pie dish.
5. Pour the filling into your pie dish and brush some of the beaten egg around the edges of the dish.
6. Cover your pie with the puff pastry lid and seal the edges with your fingertips or a fork. Brush the pastry lid with the rest of the egg and add a couple of slits in the centre with a sharp knife.
7. Bake for about 35 minutes or until the pastry is golden brown and crispy.