Halve the kidneys and cut out the tubes. Rinse in cold water and peel off the skins. Cut in small pieces. Trim and cut the steak in cubes.
Heat oil and butter in a large pan, then fry the onions for 3-4 minutes, stirring. Fry the meat for 2-3 minutes until it loses its pink colour. Stir in the flour and cook for 2 minutes. Add the herbs and stock. Stir until thickened and coming to the boil.
Add mushrooms and puree, lower the heat and simmer, covered, for about 1 and a half hours until, the meat is tender.
When the meat is cooked, remove bay leaves, season with salt, pepper, Worcestershire sauce, then cool slightly.
Roll out the pastry on a floured surface to ¼" thick and 1" wider then a 1.2 Litre/2 pint pie dish. Cut out the lid so it is slightly bigger than the dish. Cut a strip of pastry the width of the rim. Stir the parsley in to the meat and transfer to the dish.
Brush the rim with egg, lay pastry strip on top and seal. Brush with egg and put lid on top. Seal the edges, knock them up with the back of a knife. Flute the edge. Cut a slit in the lid, brush with the egg (but not the edges or they won’t rise).
Bake for 20 minutes, then brush with egg again. Bake for 10 minutes until the pastry is golden