Preheat your oven to 200°C (390°F). Take the beef fillet out of the refrigerator at least 30 minutes prior to cooking, allowing it to come to room temperature. This ensures even cooking throughout.

Season the beef fillet generously on all sides with salt and freshly ground black pepper. For an extra layer of flavour, you can brush the fillet with Dijon mustard, ensuring the mustard coats the meat evenly.

Heat 2 tablespoons of olive oil in a heavy-bottomed ovenproof skillet over medium-high heat. Once the oil is hot and shimmering, carefully place the beef fillet in the pan. Sear for 2-3 minutes on each side until a golden-brown crust forms. Avoid moving the fillet too much while searing to develop a deep, rich crust.

Add the unsalted butter, fresh thyme sprigs, and crushed garlic to the skillet. As the butter melts, use a spoon to continuously baste the fillet with the butter, ensuring it absorbs the herb-infused flavors.

Once seared, transfer the skillet to the preheated oven. Roast the beef fillet for 10-12 minutes for medium-rare, or adjust the cooking time depending on your desired doneness (use a meat thermometer: 54°C / 130°F for medium-rare, 60°C / 140°F for medium).

Remove the skillet from the oven, carefully transferring the beef fillet to a cutting board. Let it rest for 10-15 minutes. Resting allows the juices to redistribute within the meat, ensuring each bite is juicy and tender.

While the beef rests, prepare any accompanying sauces or sides. Chateaubriand is traditionally served with a béarnaise sauce or red wine reduction, and classic sides like roasted potatoes or sautéed vegetables complement the dish perfectly.

To serve, slice the Chateaubriand into thick, even medallions. Garnish with fresh parsley for a touch of colour and flavour. Present the beef fillet with your chosen sides and sauce. A drizzle of the butter and thyme mixture from the skillet over the meat adds a final flourish of flavour.