2. Heat the olive oil in an ovenproof non-stick skillet over medium heat.
3. Peel the potatoes and cut them into very thin slices. Layer half of the potatoes in overlapping slices to cover the bottom of the pan.
4. Sprinkle with the oregano or parsley, garlic, manchego cheese, salt and pepper. (Be careful not to sprinkle the cheese on the side of the pan, or it may stick.) Add the remaining potatoes in overlapping slices and sprinkle with salt and pepper.
5. Cover the skillet with foil and place it in the oven and cook until the potatoes are tender, about 15 minutes.
6. Remove the skillet from the oven, remove the foil, carefully loosen the edges of the potatoes and turn the tart onto a plate or platter. Cut the tart into wedges and serve.