Toss the beef cubes and chopped kidneys in the seasoned flour until they are evenly coated, shaking off any excess.

Heat the vegetable oil in a large Dutch oven over medium-high heat and sear the meat in batches until deeply browned on all sides, about 5 minutes per batch, then transfer to a plate.

Reduce the heat to medium, add the chopped onion, carrots, and garlic to the same pot, and cook for 5 minutes until the vegetables begin to soften and turn fragrant.

Pour in the Irish stout beer, scraping up any browned bits from the bottom of the pot, then stir in the beef broth, Worcestershire sauce, and fresh thyme sprigs.

Return the browned meat to the pot, bring the mixture to a simmer, then cover and cook over low heat for 90 minutes until the meat is melt-in-your-mouth tender.

Preheat your oven to 400°F (200°C), transfer the cooked meat filling into a 9-inch deep-dish pie plate, and let it cool slightly while discarding the thyme sprigs.

Drape the puff pastry sheet over the pie dish, trim the excess edges, crimp to seal, and cut a small slit in the center to allow steam to escape.

Brush the top of the pastry generously with the beaten egg wash to ensure a shiny, beautifully golden-brown crust during baking.

Bake for 25 to 30 minutes until the puff pastry is puffed and golden brown, then serve hot alongside creamy mashed potatoes and steamed green peas.