Scottish Steak, Potato & Leek Pies

olive oil
400 gm centre cut piece of fillet steak (or rump or porterhouse), well trimmed & cut in 3 or 4
2 cups diced & peeled chats (baby potatoes)
2 cups chopped leeks
beef stock
2 spring (green) onions, chopped
2 tbsp HP sauce
1 tspn English mustard
sea salt flakes
freshly ground pepper
olive oil spray
4-6 frozen puff pastry sheets, thawed a little
1 egg
¼ cup milk
Heat a little oil in a large frypan and briefly cook steaks to just seal all over. Remove and set aside. Turn heat down and add chats and leeks. Gently cook, covered, until very tender, adding a little stock halfway through the cooking process. (Mix should be fairly dry at end.) Then cube steak and add to pan along with spring onions, HP sauce, mustard and seasonings. Mix well and cook for about 2 mins. Then turn off heat. Preheat oven to 190°C-200°C. Beat egg and milk to make eggwash. Then place a pastry sheet on a lightly oiled baking tray, overlapping over one side. Put mix along one half crossways and then fold up, crimp the edge with a fork and brush with eggwash. Repeat the process. Sprinkle a little salt on top, if you like, and cook in the oven for about 15-20 mins until golden.