Heat oil in large saucepan, and add the onion and cook until soft.
Add the beef and kidney until browned. Add the flour and cook stirring for 1 minute. Add the stock and sauce, salt and pepper and bring to the boil. Partially cover and simmer for 2 hours.
Add the mushrooms and cook for 30 minutes or until the meat is tender.
Make the pastry. Sift the flour and add the butter and rub in until it resembles breadcrumbs. Add the water and mix until the dough comes together to form a ball.
Roll out onto a floured surface, about 1 inch thick and that is larger than the pie dish.
Spoon the meat mixture in your pie dish and cover with the pastry. Make a hole in the middle so the steam can escape. Crimp the edges with a fork and decorate with any leftover pastry trimmings. Brush the top with the beaten egg.
Bake in a preheated oven 180°c fan/200°c/Gas 6 for 30 minutes until the pastry is crisp and golden.
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