8 or 9 eggs
1 kg potatoes
extra virgin olive oil
2 medium onions (optional for the tortilla)
Wash, peel and cut the potatoes into thin slices. Place them in cold oil with a little salt and cook for 40 minutes over medium heat or until they are soft when pricked with a fork. Drain them in a colander and set aside.
If you want onion in your tortilla you can add it to the pan with the potatoes or caramelize it in a separate pan over a very low heat for 1.5 hours until brown. Stir constantly.
In a bowl, mix the eggs and add the potato (or potatoes with onion or caramelized onions as required) and a little salt. Mix together well.
Heat a frying pan over a medium heat with a little oil and pour in the mixture. When bubbles start to appear in the centre turn the tortilla over with the aid of a saucepan lid or flat plate. If necessary, add a drizzle of oil before doing so. After a couple of minutes the tortilla will be ready if you want it to be still runny in the middle, the longer you leave it the firmer it will be.
Cut into triangles or squares to serve.