This is such a simple recipe and really makes a great holiday meal. Serve the steak whole in the middle of the table for a dramatic showstopper or slice and plate individually.
Technique tip: Use a thermometer to take the temperature the meat and use the range from medium-rare to well done. Know that the ends of the meat will always be more cooked through for those who like slices more well done.
Preheat oven to 375°F.2.
Cook the tenderloin: Heat a cast-iron skillet large enough to hold the beef until it begins to visibly smoke. Season the steak on all sides with salt and pepper. Shut the heat off underneath the skillet, add the oil and use a pair of tongs to place the steak in the pan. Turn the heat on under the skillet and brown on the first side, 3-5 minutes. Turn the steak and brown on all sides for a total of 12-15 minutes.3.
Transfer the steak to a baking sheet and place in the oven to finish cooking. The internal temp, in the center, should be about 130°F-135°F for medium rare. Remove from the oven and let it rest for about 15 minutes.4.
Remove the excess grease from the pan where you cooked the steaks. Add the butter and the shallots and cook until translucent, 5-8 minutes. Add the brandy and cook until the liquid reduces almost completely, 3-5 minutes. Add the stock and reduce by about half. Add the mustard, Worcestershire and vinegar. Swirl the pan and simmer 1-2 more minutes so all of the flavors meld together. Taste for seasoning. Reduce the sauce more, if needed.5.
Place the tenderloin on a flat surface, slice and arrange the meat on a serving platter. Serve the sauce spooned on top and on the side. Top with the parsley.