Prepare the kidneys by soaking them in cold water for 30 minutes, then drain and pat dry. Cut the kidneys in half, remove the white fatty core, and chop into bite-sized pieces.

In a large Dutch oven or heavy-bottomed pot, heat 1 tablespoon of vegetable oil over medium-high heat. Season the beef chuck cubes with salt and pepper, then brown them in batches for 4-5 minutes until seared on all sides. Transfer the beef to a plate.

Add the remaining tablespoon of oil to the pot, then add the chopped kidneys. Sear for 2-3 minutes until lightly browned, then transfer them to the plate with the beef.

Reduce the heat to medium and add the chopped onion to the pot. Sauté for 5 minutes until softened and translucent, scraping up any browned bits from the bottom of the pan.

Sprinkle the flour over the onions and stir well, cooking for 1 minute to remove the raw flour taste. Gradually pour in the beef broth and dark ale, stirring continuously until the sauce begins to thicken.

Return the beef and kidneys to the pot, along with the Worcestershire sauce and fresh thyme. Bring the mixture to a gentle simmer, cover, and cook on low heat for 1.5 hours, or until the meat is completely tender.

Preheat your oven to 400°F (200°C). Transfer the meat and gravy filling to a 9-inch pie dish and let it cool slightly for about 10 minutes.

Roll out the thawed puff pastry sheet so it is slightly larger than your pie dish. Place the pastry over the filling, crimp the edges to seal, and brush the top generously with the beaten egg. Cut a small slit in the center to allow steam to escape.

Bake the pie for 25-30 minutes, or until the pastry is puffed, crisp, and deep golden brown. Let it rest for 10 minutes before slicing, and serve hot with mashed potatoes and buttery peas for a classic British meal.