2 teaspoons of truffle oil, optional but highly recommended
1 jellyroll pan lined with parchment paper (you may need a second pan, depending on the size of your potatoes)
Preheat oven to 425º F. Peel potatoes and cut a tiny slice cut off at each end, to flatten. Slice potatoes crosswise into ½-inch thick pieces (4-5 slices per potato) Count the number of potato slices to determine how many slices of steak you’ll need (*see below)
In a small bowl, combine garlic powder, onion powder, paprika, ½ teaspoon salt, and ½ teaspoon pepper. Place potato slices in a large bowl with 3 tablespoons of oil and toss to coat. Sprinkle on spice mix and toss. Arrange potato slices in a single layer on parchment-lined pan. Bake for 20 minutes, until tender. Remove from the oven and tent with foil.
Before slicing the tenderloin, determine how many pieces you need. *There are two pieces of steak and 3 slices of potato in each stack. (For example: 8 stacks require 24 slices of potato and 16 pieces of steak) The steak should be about the same thickness as the potatoes so I suggest starting by using a very sharp knife to slice the tenderloin horizontally into ½ inch thick slices. Then cut it into however many smaller pieces you need.
Sprinkle meat with 1 teaspoon of salt and 1 teaspoon of pepper. In a large cast iron skillet or non-stick pan, heat 1 tablespoon of oil over medium-high heat. When the oil is hot, add half the steak pieces. Cook for 1 ½ - 2 minutes per side for medium rare. Transfer to a plate and repeat with remaining steak.
Assemble the stacks on a serving platter with the largest pieces of potato on the bottom. Place the largest pieces of steak on top, then the medium sized pieces of potato, then the rest of the steak, and top with the smallest pieces of potato. Drizzle each stack with ¼ teaspoon of truffle oil, and top with a generous pinch of tarragon. Serve warm or at room temperature.