This pie is a real winner! As it uses bought puff pastry, it’s quick to prepare, and you can make the filling the day before if you want. For a bit of a treat you could use 500g of pastry and line the bottom of the pie dish - just make sure you cook it at the bottom of the oven so the pastry has a chance to crisp up.
Preheat the oven to 190ºC/375ºF/gas 5. In a large ovenproof pan, heat a lug of olive oil on a low heat. Add the onions and fry gently for about 10 minutes – try not to colour them too much. Turn the heat up, add the garlic, carrots and celery and scatter in the mushrooms. Mix everything together before stirring in the beef, rosemary, a pinch of salt and a level teaspoon of pepper.
Fry fast for 3 or 4 minutes, then pour in the Guinness, stir in the flour and add just enough water to cover. Bring to a simmer, cover the pan with a lid and place in the preheated oven for about 1½ hours. Remove the pan from the oven and give the stew a stir. Put it back into the oven and continue to cook it for another hour, or until the meat is very tender and the stew is rich, dark and thick. A perfect pie filling needs to be robust, so if it’s still quite liquidy, place the pan on the hob and reduce until the sauce thickens. Remove from the heat and stir in half the cheese, then season carefully and leave to cool slightly.
Dust a clean work surface with flour and roll the pastry out evenly with a floured rolling pin to the thickness of a pound coin. Tip the stew into your dish and even it out before sprinkling over the remaining cheese.
Place the pastry over the top of the pie dish and criss-cross it lightly with a sharp knife. Brush the top with beaten egg, then bake the pie directly on the bottom of the oven for 45 minutes, until the pastry is cooked, puffed and golden. Delicious served simply with peas.