Meat and potato pastry pie

Method

1. Heat the oven to 140°C fan/gas 3. Toss the beef with the flour and a generous amount of salt in a bowl until the beef is well coated. Put all the filling ingredients up to and including the rosemary in a large, shallow, hobsafe casserole with a lid, then pour in 700ml water. Bring to a simmer on the hob, put the lid on, then cook in the oven for 2 hours. Put the potatoes in the oven at the same time.
2. After 2 hours, remove the potatoes from the oven, check they’re cooked and soft by prodding them with a table knife, then leave to cool a little. Stir the mushrooms into the casserole, put the lid back on and cook for another hour.
3. Once you can handle the potatoes, peel them carefully, then roughly chop – you should have around 300g flesh. Put this in a food processor and whizz to a smooth pulp. It will be gloopy – don’t worry. Add the butter and flour with a large pinch of salt, then pulse briefly until it comes together into a dough (it will feel similar to hot water crust pastry). Tip it out of the processor and knead briefly on a work top, then shape into a fat rectangle, wrap tightly and leave to cool, then chill for an hour.
4. Once the casserole has had 3 hours in the oven and the beef is tender, remove the lid, turn the oven off and set the casserole on the hob over a medium-high heat. Bring it to a simmer, adding the wine or beer if you’re using it, and bubble to reduce for 10-15 minutes until it’s the consistency you want – quite saucy is good. Tip the filling into the pie dish and leave to cool for at least an hour.
5. Once the pastry has chilled, heat the oven to 180°C fan/gas 6. Unwrap the pastry and put on a lightly floured surface. Roll it out with a floured rolling pin (it won’t be like normal pastry – more like bread dough) to around 0.5cm thickness and a bit larger than your pie dish. Brush the edges of the dish with beaten egg, then roll the pastry loosely around your rolling pin and unravel it over the pie dish.
6. Cut off any overhang, then reroll and stamp out shapes to decorate the top, if you like. Crimp the edges and press to seal. Cut a steam hole in the centre, then brush the top with egg. Bake in the middle of the oven (on a baking tray in case of spills) for 35-40 minutes until the filling is bubbling and the pastry is deep golden all over. Cover loosely with foil if the top is browning too quickly.
7. Once baked, leave the pie to stand for 5 minutes before serving with plenty of green veg.