1/2 cup olive oil, or a combination of olive oil and vegetable oil
3 large baking potatoes, peeled and cut in 1/8 inch slices, easy on a mandoline slicer
1 large onion sliced
4 large eggs
salt and pepper
In a 9 inch skillet, heat oil and layer potatoes and onions, salt and pepper between each layer. Heat over medium heat, the potatoes should boil rather than fry. Turn while cooking until tender being careful not to brown. Drain in colander and reserve the oil.
Beat the eggs and add to the potato mixture. Let set for 15 minutes. Heat 3 tablespoons of the reserved oil until hot. Add the potato mixture. When browned, and you can shake the pan to make sure the tortilla is not sticking, turn onto inverted plate. Add 1-2 tablespoons of oil to pan and cook the other side. If necessary, flip a couple of times to brown evenly and set. ( I find the less you have to flip, the easier it is not to make mistakes.) Cool. Cut into wedges or squares. Can be prepared ahead…tastes betters and cuts more easily. Also freezes well.