Preheat oven to 400 degrees F. Drizzle the tenderloin with oil. Season well with plenty of salt and pepper. Sprinkle with assorted fresh herbs. Allow the tenderloin to come to room temperature before cooking. Place a large cast-iron skillet over medium-high heat and sear tenderloin on all sides (add additional oil, if necessary). Place the skillet in the preheated oven and roast the tenderloin for about 15 to 17 minutes. (At this point, a meat thermometer inserted into the thickest part of the meat should read 135 degrees F for medium rare; for medium, roast for 3 minutes more.) Remove from the oven. Tent tenderloin with foil; allow to rest for 10 minutes before slicing. Serve with Blender Bearnaise (see below). If you like, garnish with watercress.

To make the reduction for the bearnaise sauce, combine vinegar, wine, shallot, and half of the tarragon in a small saucepan and place over medium-high heat. Bring to a simmer and cook until reduced by half. Remove from heat and set aside to cool. Blend yolks and bearnaise reduction together in a blender on low speed until combined. With the blender running on medium speed, add one-third of the butter in a slow, steady stream. Once the mixture emulsifies (it will become thick and satiny), turn the blender speed up to high and add the remaining butter. Add the remaining tarragon, season with salt and pepper, and pulse in the blender. Transfer to a dish; hold in a warm spot until ready to serve.