For the pastry, sift the flour and the salt into a large mixing bowl, then put into the fridge for a few minutes to chill. (Keeping the flour and bowl cold will help you to get a better result later and create nice separate layers or pastry.)
Meanwhile, cut the butter into small cubes.
Using a round-bladed knife, stir the butter into the bowl until each piece is well coated with flour.
Pour in the water, then, working quickly, use the knife to bring everything together to a rough dough.
Gather the dough in the bowl using one hand, then turn it onto the work surface. Squash the dough into a fat, flat sausage, without kneading. Wrap in cling film then chill the dough in the fridge for 15 minutes.
Lightly flour the work surface and the pastry. Roll out the pastry in one direction until it’s about 1cm thick and three times as long as it is wide, or about 45x15cm/18x6in. Straighten up the sides with your hands now and again, and try to keep the top and bottom edges as square as possible.
Fold the bottom third of the pastry up, then the top third down, to make a block about 15x15cm/6x6in. It doesn’t matter if the pastry isn’t exactly the right size - the important thing is that the corners are nice and square.
Turn the dough so that its open edge is facing to the right, like a book. Press the edges of the pastry together with the rolling pin.
Roll out and fold the pastry again, repeating this four times in all to make a smooth dough, with buttery streaks here and there. If the pastry feels greasy at any point, or starts to spring back when as you roll, then cover and chill it for 10 minutes before continuing.
Chill the finished pastry for an hour, or ideally overnight, before using.
For the filling, mix the beef with the flour and some salt and pepper. An easy way to do this without making too much mess is to put everything into a large food bag, seal, then shake well.
Heat a tablespoon of the oil in a large heatproof casserole up to a medium heat, then add half of the beef, shaking off the excess flour and keeping the chunks well-spaced so they fry rather than sweat. Brown for about 10 minutes, until golden-brown all over.
Transfer the first batch of meat to a bowl, then add a splash of brown ale or water to the pan and scrape up any meaty bits. Tip the liquid into the bowl of meat. Wipe out the pan, then add a tablespoon of oil and brown the second batch of beef. When the beef is golden-brown transfer it to the bowl and set aside.
Chop the garlic, onion, carrots and celery into chunky pieces. Add the final spoon of oil to the pan and heat gently. Add the vegetables and herbs to the pan and fry to soften for a few minutes.
Put the beef back into the pan. Pour in the stock and brown ale, then add the tomato purée and balsamic vinegar. If necessary, add a little more stock or hot water to ensure the meat is covered in liquid (this will prevent the beef from drying out). Bring to the boil then cover and simmer the stew for 1-1½ hours until the beef is almost tender and the sauce has thickened.
Set aside to cool, overnight if possible.
Melt the butter in a large frying pan, then add the mushrooms (cut into halves, or quarters if large). Season with salt and freshly ground black pepper, then fry over a high heat for about five minutes, until golden-brown. Mix with the cooled pie filling and add to the pie dish.
To make the pie, preheat the oven to 200C/400F/Gas 6. Flour the work surface, then roll out the pastry to the thickness of two £1 coins and wide enough to cover a family-size pie dish with some excess.
Brush the edge of the pie dish with a little water or beaten egg.
Use a sharp knife to cut the pastry to fit the top of the dish – if it’s too big it doesn’t matter. Lift on top of the pie, laying the pastry over a rolling pin to lift it. Press down gently to seal.
Holding the knife blade horizontally, make a patterned edge by pressing down gently all around the edge of the pastry (this will help the layers in the pastry to puff up).
Cut a couple of slits in the top of the pie to release steam. Brush the top of the pie with the beaten egg – taking care to avoid getting egg on the edges of the pastry as it will stick the layers together.
Chill for 10 minutes, or until the pastry is firm.
Bake for 30 minutes, or until the filling is bubbling and the pastry is golden-brown and puffed all over.