Preheat the oven to 425˚F.
Set a large skillet over medium-high heat. Add a drizzle of oil and sauté the onion and ground sirloin and cook, breaking up the meat with a spoon until it’s no longer pink.
Stir in the Worcestershire sauce, tomato paste, potato and peas and cook for another 2-3 minutes, until the mixture is well blended and any excess moisture has cooked off.
On a lightly floured surface, roll the puff pastry out into a 10-inch square, and cut into four squares. Transfer to a parchment-lined baking sheet and divide the filling between the squares.
Brush around the edge with some beaten egg and fold over to seal, pressing around the edges with the tines of a fork.
Poke the top of each pie once or twice, and brush all over with beaten egg.
Bake for 20-30 minutes, until deep golden.