- Place the Chateaubriand in the freezer. If you are concerned about bacteria, sear the meat very quickly on all sides before placing in the freezer. Keep in the freezer until almost frozen through.
- Mix the mustard and the mayonnaise together and set aside.
- Once the beef is almost frozen through, pull out of the freezer and slice as thin as you can with a meat slicer or a sharp knife. Arrange slices, slightly overlapping on a very cold plate. Work quickly before the meat thaws.
- Sprinkle the meat with a coarse salt, such as Maldon Sea salt, or Fleur de sel. Crack some fresh pepper over it and then drizzle with a little bit of extra virgin olive oil.
- Garnish the plate with the mayonnaise mustard mix, red onions, and capers.
- Serve immediately.