Peel the potatoes and chop them finely in a bowl, around 2 mm thick.
Chop the onions and add it to the potatoes, add salt to taste and mix it. Put a large non-stick frying pan on a high heat, add olive oil until it covers the base (yes, we use a lot of olive oil). Add the potato mixture and the garlic in the oil until soft but not brown – this should take about 20-25 mins. Do not forget to stir the mixture, crushing sometimes the potatoes, this will help the starch to thicken the mixture. You know it will be ready when the potatoes are soft.
Beat the eggs in a bowl. Separate the potato mixture from the oil and add the potatoes to the eggs and mix well. Using the same pan, with a drizzle of olive oil put it on high heat and wait until it is hot, then add the eggs and potatoes.
Move the pan to prevent from sticking in the base and when the edges are starting to be cooked (about 2-3 minutes) turn it over with a plate and put it back to the pan. Move from time to time the pan and when you see the tortilla moving from the base it means it is ready.
Transfer the tortilla to a plate and wait 10 minutes, it will allow the tortilla to cook from inside and preventing from drying it completely. You can serve it as a tapa with a fresh beer or wine or a main course with a bit of salad.