The most tender and valuable cut of marbled beef is the Tenderloin, and Chateaubriand is its central part. Fried and then baked beef fillet in European cuisine is traditionally served with creamy or wine sauces.
You can add balsamic vinegar, rosemary and some meat stock to your liking. And it is better to choose fortified wine. For example, Merlot or Cabernet. But the general principle is that you need to prepare the sauce only from high-quality wine, which you enjoy drinking from a glass. Especially if the sauce is being prepared for meat like Chateaubriand.