Preheat your oven to 200°C (390°F).
In a large bowl, toss the chunks of beef with flour, salt, and pepper until they're well-coated.
In a Dutch oven or large oven-proof pot, heat the olive oil over medium-high heat.
Brown the beef in batches to avoid overcrowding; this should take about 3-5 minutes per batch.
Once browned, transfer the beef to a plate and set aside.
In the same pot, add the onions, carrots, celery, and garlic, cooking until soft, about 5 minutes.
Stir in the tomato puree and cook for another minute.
Pour in the Guinness or ale, beef stock, and Worcestershire sauce, then add the thyme leaves.
Return the browned beef to the pot, cover, and cook in the oven for about 1.5 hours, or until the beef is tender.
Transfer the stew to a pie dish, letting it cool slightly.
Roll out the pastry to cover the pie dish.
Place the pastry over the filling and trim any excess.
Press the edges to seal and make a small slit in the center to allow steam to escape.
Brush the pastry with the egg wash.
Bake in the oven for 15-20 minutes or until the pastry is risen and golden brown.