Add the oil to a large pan over medium heat. Add the onion and gently fry until soft and starting to turn golden, then add the garlic and fry for a minute longer. Add in the beef and fry until browned, breaking it up with your wooden spoon as you go.
Stir in the flour until well combined, then gradually pour in the stock, stirring as you go to prevent lumps from forming. Stir in the Worcestershire sauce, ketchup, Oxo cube, onion powder and white pepper and bring to a simmer. Lower the heat slightly and simmer for around 25 minutes until the gravy is nice and thick, stirring occasionally. Cool for 10 minutes. Meanwhile, preheat the oven to 200C/400F.
Slice the tops off of the rolls and use your hands to press the filling to the outside and bottom of the roll. This will form a protective layer to prevent the roll from going soggy. Spoon in the filling, then slice out 5 circles from the pastry the same size as the rolls and press them on top of the rolls.
Place the pies on a large baking tray, brush the bread with butter and then the pastry with beaten egg. Slice a couple of steam holes in each pie, then place them in the oven until the pastry is deep golden and crispy (usually 18-20 minutes).
Slice in half then tuck in!