I was taught to cook it with a pancake around the beef, to seal the juices of the beef and also the liquid from the mushrooms.
A previous example had shown a professional chef using a pancake.
It is easy to cook medium or well done, just roast the beef instead of just browning it, roast it for about 50 minutes less than you would normally cook it, let it rest remembering it will continue cooking whilst resting then you can wrap and re-roast with the pastry.
I do individual ones for people to home cook at dinner parties, using different designs of pastry on top so clients can tell the difference when dishing up.