- Blot the tenderloin and put it on a cutting board, straightening it as much as possible. Using a very sharp knife with a long, thin blade, carefully cut the tenderloin crosswise into 1-inch slices. Shape each round to be as even as possible before placing it on a rack to dry. Because tenderloin tapers at both ends, the last two pieces will not be round. Combine them into one piece, using a piece of kitchen twine or toothpicks to hold them together in a yin and yang pattern. Salt the medallions lightly on top and air-dry them at room temperature for about 1 hour.
- Choose a heavy sauté pan or cast-iron griddle large enough to hold all the medallions in one layer. Melt the butter and oil in the pan over medium heat until the mixture is fragrant and liquid. Place the medallions in the hot fat (they should sizzle), and fry for about 3 minutes on the first side and 2 minutes on the second side, or until cooked in the center and browned and crisp on the outside. Using tongs, transfer the meat to a platter to rest.
- Make the sauce by deglazing the pan with the vermouth, scraping up any browned bits and boiling off the alcohol to reduce the volume by half. Turn off the heat and stir in the orange zest, mustard, and cream. Spoon this over the medallions and serve at once, showered with a little parsley.