Heat the oil in the Dutch oven; add the onion until translucent, about 2-3 minutes. Add the garlic and cook for 1 minute. Add the ground beef and cook until no pink remains, about 5-6 minutes. Stir in the salt and pepper; sprinkle the flour over the beef and cook for another minute. Pour in the stock and Worcestershire sauce and simmer until the gravy has reduced and thickened, about 6-8 minutes. Scrape the beef mixture into a bowl and let cool to room temperature. Cover and refrigerate until completely chilled, at least 1 to 2 hours.
Remove the puff pastry from the refrigerator and roll the sheets to 1/8- inch thick. Cut the pastry into twelve 4-inch rounds and twelve 3-inch rounds. Place on a baking sheet lined with parchment and refrigerate for 30 minutes.
Lightly grease a 12-cup muffin tin. Press the larger puff pastry rounds in the base of each muffin tin, so they are flush with the bottom and sides of the tin and slightly overlap the rims. Stir the cheese into the beef mixture, and evenly divide the filling between each pie.
Whisk the egg in a bowl. Brush the edges of the pastry overlap with the egg mixture and fold over the top of the meat; top with smaller pastry rounds and use the remaining egg to brush the tops of each pie. Place the tin in the refrigerator to cool for 15 minutes before baking.
Add the convEGGtor for indirect cooking at 425ºF/218ºC. Bake the pies for 20-25 minutes until golden brown. Cool 10 minutes before serving.