Peel the potatoes. Divide them in half. Cut in half moon shape, very thin. (around 2-3 milimeter. You can use the ruler on the right top corner) Wash the slices under cold water and dry.
Chop the onion into small cubes.
Take 2 tbsp of olive oil to the pan and start to sautée onions in medium heat, for 2-3 min. Then add the potatoes that you have season with salt and pepper. Add 2 tablespoon of olive oil to the pan.
Until the potatoes are tender continue cooking, around 10-15 min. (In the meantime, you can prepare the salad. Recipe below)
Break the eggs into the mixing bowl and add a pinch of salt, pepper.
After stirring thoroughly, take the potatoes (be sure they are cooked) and onions into the egg, stir them.
Add the butter to the same pan and melt it over medium heat.
Pour the potato and egg mixture over the hot oil.
Cook until the egg is solistified. Give shape to the edges of the omelette with a spatula to preserve its rounded shape and thickness.
After the base is cooked, close the top of omelette with a plate. (Inside of the plate should touch the omelette) By holding the handle of the pan with one hand, push the plate with the other hand, turn them and take the omelette on the plate. Slide the omelette you made upside down, from the plate into the pan and bake this side of it.
Serve your cooked Spanish Omelette by slicing them like cake or pizza.
For the salad;
Wash mediterranean greens in plenty of water. Divide cherry tomatoes into 4. Slice radish very thinly, peeling or without peeling. Mix the ingredients in the mixing bowl.
Before serving, add 2 tbsp extra virgin olive oil and add a pinch of salt.