Begin by seasoning the beef cubes generously with salt and freshly cracked black pepper to enhance their natural flavors. Warm a tablespoon of olive oil in a heavy frying pan over high heat, then carefully sear the meat in three batches. This ensures each piece is browned beautifully without overcrowding, creating a rich caramelized crust that seals in juices. Once browned, transfer the beef to a large flameproof casserole dish to prepare for slow cooking. Remember to add extra oil if your pan gets dry during this process. Using the same pan, add another tablespoon of olive oil and gently cook the shallots for 4 to 5 minutes until they soften and release their sweetness. Add the minced garlic, frying for 30 seconds to awaken its aroma, then toss in the bacon pieces, cooking until they're lightly browned and start to crisp around the edges. This mixture adds a smoky, savory base to the pie's filling. Transfer the shallots, garlic, and bacon to the casserole with the beef, then stir in the chopped thyme and bay leaves to infuse fragrant herbal notes. Preheat your oven now to 180°C (350°F or Gas mark 4) to prepare for the slow roast. Pour the stout into your frying pan, bringing it to a gentle boil while stirring to loosen those delicious caramelized bits stuck to the bottom — this adds intense flavor depth. Pour this rich liquid over the meat in the casserole, then add the beef stock to create a hearty braising sauce. Cover the casserole tightly with a lid and place it in the oven, allowing the beef to cook slowly for 1½ to 2 hours until it's beautifully tender and the sauce has thickened and reduced. Once cooked, carefully skim off any fat that has risen to the surface for a cleaner taste. Taste your filling and adjust seasoning with salt and pepper as needed. Next, mix the cornflour with a splash of cold water to create a smooth paste, then stir this into the hot filling on the stove over low heat. Simmer gently for 1 to 2 minutes, stirring continuously, until the sauce thickens into a luscious consistency. Set the filling aside to cool. Meanwhile, increase your oven temperature to 200°C (400°F or Gas mark 6) to prepare for baking the pie. To make the pastry, place the plain flour and a pinch of salt into a large bowl. Grate the cold butter into the flour in three batches, folding it in to achieve a crumbly texture reminiscent of fine breadcrumbs. Gradually add the cold water, about 325ml, stirring with a round-bladed knife just until the dough begins to come together. Be careful not to overwork — you may not need all the water. Lightly knead the dough on a floured surface into a smooth ball. Set aside approximately 250g of the dough to use for the pie lid, refrigerating it while you roll out the base. Roll out the remaining dough into a circle roughly 2cm (¾ inch) larger than your pie dish. Line the dish carefully with the pastry, pressing gently to fit it snugly without stretching. Spoon the cooled beef and oyster filling into the pastry shell, nestling the oysters among the meat for hidden bursts of delicate sea flavor. Brush the exposed edges of the pastry with beaten egg to help seal the lid. Roll out the reserved pastry slightly larger than the dish and gently place it over the filling. Press the edges together firmly to create a sound seal, then trim any excess dough with a sharp knife for a neat finish. Brush the entire surface of the pastry lid with beaten egg — this glaze encourages a shiny, golden crust. Place your pie dish on a baking tray to catch any drips and bake in the preheated oven for 25 to 30 minutes. Bake until the pastry is a beautiful golden-brown and the filling is bubbling enthusiastically beneath, signaling it's ready to be enjoyed. Let the pie rest a little before serving to allow the filling to set slightly for perfect slices. Enjoy this comforting classic with family or friends!