- 6 tablespoons olive oil, divided
- 1 2 1/4-pound beef tenderloin (preferably from thick end)
- 1 1/2 teaspoons coarse kosher salt
- 2 teaspoons coarsely ground mixed peppercorns
- 1/4 cup Sherry wine vinegar
- 1 tablespoon coarse Dijon mustard
- 1/4 cup chopped shallots
- 1 large bunch watercress
- Preheat oven to 500°F. Rub 1 tablespoon olive oil into beef, then rub in kosher salt and ground mixed peppercorns. Place beef on small rimmed baking sheet. Roast 10 minutes. Reduce heat to 450°F and roast until thermometer inserted into thickest part of meat registers 125°F for medium-rare, about 15 minutes longer. Let meat stand 5 minutes (internal temperature of meat will increase 5 to 10 degrees).
- Meanwhile, whisk remaining 5 tablespoons olive oil, vinegar, and mustard in small bowl to blend. Stir in shallots and season vinaigrette to taste with salt and pepper.
- Arrange watercress on small platter. Cut meat into 1/2-inch-thick slices; arrange overlapping slices atop watercress. Drizzle any accumulated juices over meat. Spoon half of vinaigrette down center of meat and over watercress. Serve, passing remaining vinaigrette separately.