Heat 1 tablespoon olive oil in a skillet over medium heat and sauté the diced onion and minced garlic until softened.
Add the ground beef and cook until browned, breaking it apart as it cooks.
Stir in beef stock, Worcestershire sauce, tomato paste, and thyme. Simmer for 10–15 minutes.
Mix in a cornstarch slurry to thicken the gravy, then allow the filling to cool slightly.
Line pie tins with shortcrust pastry and fill each with the beef mixture.
Cover with puff pastry, trim the edges, seal with a fork, and cut a small steam vent on top.
Brush with beaten egg and bake at 400°F (200°C) for 25–30 minutes, or until golden brown.
Let cool for 5 minutes before serving.