For the pastry:
Put the flour and lard in a food processor and pulse briefly. Add the water gradually in small amounts and pulse briefly after each addition, until it just comes together to form a dough. Don’t overwork it, this step should only take a minute.
Remove the dough from the food processor, form into a rough ball using your hands. Put it in a bowl, cover with cling film and leave to rest in the fridge for about half an hour.
Divide the flour into two balls, one larger than the other. Shape each ball into a disk then roll them out with a rolling pin on a work surface dusted with flour. The larger ball should fit a large, porcelain oval pie dish and the smaller one makes the lid.
For the filling:
Preheat the oven to 160ºC.
Cut the meat into small cubes and toss in the seasoned flour. Melt the dripping in a pan and brown the meat for 2 to 3 minutes. Take the browned meat out of the pan and set aside in a large bowl. Turn off the heat.
Add the lamb stock to the pan and stir to mix in the remains of the cooked meat.
To the lamb add the onion, celery, diced carrots, leeks, thyme, a few bay leaves, a pinch of salt and pepper, and mix it all together.
Line the greased pie dish with the large pastry disk, and fill with alternating layers of sliced potatoes and the vegetable/meat mix. Don’t be afraid to heap the filling up higher than the edge of the dish. Finish with a layer of potatoes then pour over the lamb stock.
Cover with the pastry lid and pinch the edges down. Trim the excess pastry off with a knife and make a slit in the top. Brush the lid with beaten egg to glaze.
Bake in the oven for about an hour and a half at 160ºC. You can turn up the heat at the end to brown off the pastry well.
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