In a medium bowl, toss the beef cubes with the all-purpose flour, 1 teaspoon of salt, and 1/2 teaspoon of black pepper until evenly coated.

Heat the vegetable oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Brown the beef in batches for 5-7 minutes until deeply crusted on all sides, then transfer the meat to a plate.

Reduce the heat to medium, add the chopped onion to the pot, and sauté for 4-5 minutes until softened. Stir in the minced garlic and cook for 30 seconds until fragrant.

Pour in the stout beer to deglaze the pan, using a wooden spoon to scrape up any flavorful browned bits from the bottom. Add the beef broth, Worcestershire sauce, thyme, and the browned beef back into the pot.

Bring the liquid to a gentle simmer, cover with a tight-fitting lid, and cook on low heat for 1.5 hours, or until the beef is fork-tender. Stir occasionally to prevent sticking.

Once the beef is tender, gently fold in the drained oysters and simmer for just 2 minutes until their edges begin to curl. Remove from heat and carefully transfer the hot filling into a 9-inch deep-dish pie plate.

Preheat your oven to 400°F (200°C). Drape the thawed puff pastry over the pie dish, crimping the edges to seal it against the rim, and brush the top evenly with the beaten egg.

Cut three small slits in the center of the pastry to allow steam to escape. Bake for 25-30 minutes until the pastry is puffed and golden brown.

Let the pie rest for 10 minutes before slicing. Serve hot with a side of steamed green peas or buttery mashed potatoes.