||To make beef filling:
Preheat oven to 180°C.
Cut beef into 2.5cm-3cm cubes.
Season with salt and pepper, add 2 tbsp oil, and mix well.
||Heat a large frypan over a medium-high heat.
Brown the beef in 2 or 3 batches.
Remove each batch and place in casserole dish.
Reduce heat in the pan, add a little oil, add onion and mushrooms, cook for 12 minutes, and stir occasionally.
||Sprinkle in the flour and stir until the onions are coated. Gradually pour in stock and add the tomato paste, stirring well. Add the herbs, stir until the mixture boils. Add to the casserole dish, stir to combine. Cover the casserole dish, place in oven, and cook until the beef is very tender. Stir every 40 minutes or so, add water if needed to keep the ingredients just covered. Cool the beef mixture, at least until the steam has evaporated, or cool it completely if time allows.
||To make pastry:
Place the flour, salt and chopped butter in a food processor, process until the mixture is fine and crumbly.
With the motor running, slowly add the water, and process.
The mixture should begin to come together and then form a ball.
Add a little more water if needed.
Turn the pastry onto a lightly floured board, and gently knead for 30 seconds.
Cut two thirds off pastry, flatten it out to a round and cover with plastic wrap.
Flatten out remaining pastry to a small round, cover with plastic wrap.
Refrigerate both lots of pastry for 30 minutes.
||To assemble pie:
Preheat the oven to 200°C.
Take your pastry from the fridge so it warms up a little, making it easier to roll.
Roll out the larger piece of pastry to fit the base and side of a deep-sided 24cm springform tin (roll it out to an approx 35cm round).
Ease the pastry into the tin, pressing it gently against the side.
Place the cooled beef mixture into the tin.
Beat an egg and a little milk together to make an egg wash, brush the egg wash around the rim of the pastry.
||Roll the remaining smaller round of pastry out to a 23cm round. Carefully roll the pastry onto the rolling pin and ease the pastry over the filling. Trim, and then seal the edge by crimping the pastry together. Make a small slash over the top of pastry (for steam to escape). Brush pastry top with the egg wash. Decorate the top with the pastry trimmings if you like. Cook in the preheated oven for 15-20 minutes. Reduce the oven temperature to moderate, and cook a further 25-30minutes, the pie should be slightly puffed and pastry golden. Cool for 5 minutes before serving.