Preheat the oven to 200°C (400°F/Gas 6). Cut the Beef Chuck into 2–3 cm cubes, season generously with Salt and Black Pepper, then toss the meat in a light coating of Plain Flour.
Heat a large heavy-based pan over medium-high heat and add a splash of Vegetable Oil with a knob of Butter. Brown the beef in batches so it gets a good crust, transferring the browned pieces to a plate as you work.
Reduce the heat to medium and add the chopped Onion, diced Carrot and sliced Chestnut Mushrooms to the pan; cook until softened and starting to color. Add the minced Garlic and cook for another minute until fragrant.
Return the beef to the pan and pour in the Dark Ale to deglaze, scraping up all the browned bits from the bottom. Let the ale bubble for a couple of minutes to reduce slightly.
Stir in the Beef Stock, a splash of Worcestershire Sauce, a few sprigs of Thyme and the Bay Leaves. Bring to a gentle simmer, cover and cook on low for 1½–2 hours, or until the beef is very tender.
Once the meat is tender, remove the bay leaves and check the sauce consistency; if it’s too thin, mix 1 tablespoon of Plain Flour with a little cold water to make a slurry and stir it in, simmering until the gravy thickens. Adjust seasoning with more Salt and Black Pepper to taste.
Allow the filling to cool slightly so it won’t steam the pastry. Spoon the filling into an ovenproof pie dish, leaving a little room at the top for the pastry.
Roll out the All-Butter Puff Pastry to cover the dish, place it on top of the filling and trim/crimp the edges to seal. Beat the Egg and brush the pastry all over for a glossy finish; cut a couple of small vents in the top to release steam.
Bake the pie at 200°C (400°F) for 30–40 minutes until the pastry is puffed and deep golden brown. Let the pie rest for 10 minutes before serving so the filling sets slightly.
