Beef for Yorkshire pudding filling requires careful preparation to prevent overcooking during the dual cooking process. Cut tenderloin into uniform 1.5cm cubes for even cooking. Season 15 minutes before cooking to allow salt penetration. Sear quickly over high heat to develop color and flavor while keeping interior rare - the beef will finish cooking during the final oven stage. This technique prevents tough, overcooked meat while ensuring food safety. The brief final baking warms the filling and brings beef to perfect medium-rare. Quality beef tenderloin is essential as tougher cuts won't work with this quick-cooking method.