Pat the beef chuck steak as dry as possible and add to a large bowl. Season generously with salt and pepper.
Place a pot over high heat and add half of the olive oil. Add half of the beef and sear for 5-6 minutes or until deeply browned. Remove and repeat with the remaining batches. Remove beef from the pot when it’s all done.
Add the onions, celery, carrot, salt, and sauté for 6 minutes in the same pot over medium-high heat. Add the garlic and sauté for 1 minute. Add the flour and pour in the beef stock, mixing well to prevent lumps from forming.
Add concentrated tomato paste, beef stock cubes, dry red wine, Worcestershire sauce, and bouquet garni, and season well with salt and pepper. Mix and combine and bring to a boil.
Add the beef and resting juices, mix well again, and bring back to a boil. Cover the pot with a lid, reduce the heat to low, and cook for 2 hours. Remove the lid, and discard the bouquet garni. Check the seasoning and simmer for 20 minutes or until the beef is melting apart. Remove from the stovetop and let cool. This is best done overnight but can be done in 4 hours in the fridge until lukewarm.
To assemble the pies, place the cooled beef mix into the pie moulds. Cut the puff pastry slightly larger than the pie moulds. Brush the edges of the pie mould with the beaten egg and place on the puff pastry lids. Brush the top of the lids with the remaining beaten egg; optionally, you can score the top. Sprinkle with sea salt flakes and cracked black pepper.
Place the pies into the oven and bake for 25-28 minutes or until golden brown. Remove and let cool for 15-20 minutes so you don’t destroy your mouth. Dig in.