Put a large baking sheet on the middle shelf of the oven and preheat to 180°c.
For the pastry:
350g plain flour
Rub the fat into the flour, season it well and add enough cold water to bind the pastry together. Rest it in the fridge for 15 minutes or so, then roll out and line a metal pie dish. Trim the excess, then roll out again to make the pie 'lid'.
For the filling:
500g stewing beef (and see above), cubed
1 large onion, chopped
1 fist-sized potato, peeled and chopped
1 tbsp plain flour
salt and pepper
Combine all the ingredients in a bowl, mixing well to distribute the flour and seasoning evenly. Tip all this into your lined pie tin, then pour 175ml of cold water over. Top the pie with its top crust, crimp the edges together and brush the whole lot with beaten egg. Cut a couple of slits in the top of the pie to let out the steam (no need for a funnel here), then transfer to the baking tray in the preheated oven. Bake for 20 minutes, then turn the oven temperature down to 150°c and cook for a further 1 hour 15 minutes.
A dish of vegetables is all you need to to with this, then a comfy chair to sink into as you find out just why we call it idle pie.