Mum's steak and kidney pie

INGREDIENTS

• 1 large onion, diced
• Approx. 2lb (907g) stewing or braising steak, cut into rough 1 inch cubes
• 3-4 kidneys (lambs or pigs), diced without cores (ask your butcher to do this if possible)
• 3 beef stock cubes
• 6-8 tsp beef gravy granules
• 500g packet ready made pastry (we like Jus-Rol)
• a little milk or water