Heat half the oil in a large non-stick pan and fry the beef for 2 minutes, stirring once halfway through. If your pan is small, do this in two batches. Tip the meat onto a plate.
Heat the remaining oil in the pan (no need to clean) and fry the mushrooms for 2 to 3 minutes until they start to colour.
Sprinkle the paprika over the mushrooms, fry briefly, then tip in potatoes, stock and tomato sauce. Give it all a good stir, cover and simmer for 20 minutes until the potatoes are tender.
Return the beef to the pan along with any juices, and warm through. Stir in the parsley and a swirl of yoghurt and allow the steak to cool completely and place into a container to cool.
Pre-heat the oven to 200 C / Gas 6.
On a floured board, roll out pastry until it is 1 inch larger on all sides than top of the pie tins. Without stretching, press rolled out pasty into the pie tins with a quarter inch overlay on outside edge.
Using a knife cut remaining sheet of pastry and top the pies. Fill the pies with the beef and top with pastry lids, crimping and egg wash to seal the lids, pierce a small hole in the centre to allow the steam to escape.
Use any leftover pastry to make decorative shapes. Brush one side of each piece with egg and arrange pieces, egg side down, on pastry over beef.
Place the pies on a baking sheet and bake in the centre of the oven for 35 to 45 minutes. Remove the baked pies from oven and let them rest for 10 minutes before serving.