Prepare the Filling: Season the beef chunks with 1/2 tsp of salt and pepper. In a large heavy-based pot, heat 1 tbsp of olive oil over high heat. Brown 1/3 of the beef until well caramelized on all sides, then remove from the pot. Repeat this process with the remaining beef, adding more oil if necessary.
Reduce heat to medium-high, add the minced garlic and diced onion, and cook for 3 minutes until softened. Stir in the flour, then gradually pour in the beef stock, stirring constantly until the flour is dissolved. Add the red wine, tomato paste, Worcestershire sauce, black pepper, and bay leaves.
Return the beef to the pot, cover, and adjust the heat to maintain a gentle simmer. Cook for 1 hour and 45 minutes. Remove the lid and continue to simmer for an additional 30 to 45 minutes, stirring occasionally, until the beef is tender and the liquid has reduced to a thick gravy that just covers the meat. Remove from heat, cover, and allow to cool. For best results, cool overnight.
Prepare the Pastry: Preheat the oven to 180°C/350°F. Cut out 6 rounds from the shortcrust pastry and carefully drape them into pie tins without stretching the dough to avoid shrinkage (See Notes 1 & 6). Place the pies on a baking tray, top each with large sheets of parchment paper, and fill with pie weights (Note 7). Bake for 20 minutes, then remove the weights using the overhanging paper and return the crusts to the oven for an additional 5 minutes, or until they are light golden and dry. You may skip this step if desired (Note 8).
Assemble the Pies: Fill each pie crust with the cooled filling, pressing down slightly to ensure they are filled generously. Cut rounds from the partially thawed puff pastry, slightly larger than the edges of the pie bases. Brush the edges of the pie crusts with the whisked egg, then place the puff pastry lids on top, pressing the edges to seal them together. Brush the tops with the remaining egg wash, and make a small 1 cm/0.5" incision in the center of each pie lid.
Bake for 30 minutes or until the tops are deeply golden and puffed. Serve hot, with tomato sauce or ketchup if desired.