2. Thoroughly coat an ovenproof non-stick skillet with cooking spray. Drizzle two teaspoons of the olive oil in the pan and swirl to coat the entire inside.
3. Peel the potatoes and cut them into very thin slices. Beginning at the center of the pan, layer half the potatoes in overlapping slices around the pan.
4. Sprinkle with the tarragon and garlic and season with salt and pepper. Add the remaining potato slices and press down with a large spoon or spatula to compress the potatoes. Season again with salt and pepper and drizzle with the remaining olive oil.
5. Cook the potatoes over medium high heat, shaking the pan occasionally until the potatoes are crisp and brown on the bottom.
6. Place the skillet in the oven and cook until the potatoes are tender throughout, about 15 minutes.
7. Remove the skillet from the oven and carefully loosen the edges of the potatoes and turn the potato cake onto a plate or platter.
8. Sprinkle the potatoes with the fresh parsley and additional pepper. Cut into 4 equal portions.