Fry the onions for a few minutes over a medium heat to soften and add the mushrooms. Transfer to a casserole dish.
Increase the heat and brown the steak with salt and pepper, transfer to casserole.
Add the kidney to the pan for a minute and then sprinkle in the flour, stock and Worcester sauce.
Bring to the boil and then combine with ingredients in the dish.
Cover and cook for about 4 hours on Gas 3, or 8 hours on high in a slow cooker.
Transfer the mixture to a pie dish and cool and cover, ideally overnight.
In a food processor pulse the pastry ingredients together until they resemble breadcrumbs.
Add cold water and pulse until it forms a dough.
Cover in cling film and refrigerate for 20 minutes.
Roll out to cover the dish and decorate. Add a few slits to the top and glaze with beated egg..
Cook in the oven at Gas 4-5 / 180 C for about 20 minutes.