Make sure the butter and water are cold before making the pastry.
Finely dice the butter, add it to the flour and rub with your fingertips until the mixture resembles fine breadcrumbs. Make a well in the centre of the bowl and add most of the water and a pinch of salt.
Mix the dough without overworking it. You just want to bring the ingredients together.
Roll the mixture into a ball, flatten slightly and cover with cling film. Allow to rest in the fridge for at least 30 minutes. When you are ready to top the pie, roll the pastry out to a thickness of 5mm.
Cut the steak into 1 inch dice and roll in the flour, salt and pepper. Peel and dice the onion, the carrot and the celery.
Heat a large saucepan over a medium heat and add the sunflower oil. When hot, add the steak and brown on all sides. Add the diced vegetables and then the tomato purée and the thyme. Cook for 2 minutes then add the stock. Cook over a medium to low heat for 90 minutes or until the meat is tender and starting to fall apart. The sauce will have reduced and thickened as it cooks - add a little water if necessary but you are looking for a rich, thick gravy. Pour into an ovenproof pie dish.
Preheat the oven to 180'C.
Beat the egg and brush on to the sides of the pie dish. Carefully lift the pastry and place it over the filling, trim the edges away and brush the remaining egg wash on to the pastry. Transfer to the oven and bake for 25 minutes or until golden brown.
«This is a good recipe to use as a starting point. Add things like smoked bacon or use red wine as well as stock to give more flavour.»