Peel, wash and thinly slice the potatoes and cut in half into the shape of half moons. Repeat this with the Spanish onion.
Pour olive oil in a deep frying pan over a high heat - use enough oil to just cover the onion and potatoes.
Once the oil is hot, drop in a slice of onion and this should start frying immediately. Cook the onion for around 10 minutes until golden and then add the sliced potatoes. Stir occasionally for at least 15 minutes, until the potatoes are soft and cooked through.
Drain the oil from the potato and onion and mix in the egg and place into a separate dish. Let it rest for 10 minutes while you cook the chorizo and olives.
Chop the chorizo into chunks and half the pitted olives.
In the same frying pan you have used to cook the potatoes use a medium heat to cook the chorizo for 1 minute, followed by the olives for just 15 seconds before adding this to the potato, onion and egg mix.
Season and stir slowly.
To make the tortilla place a non-stick pan over a medium heat and drizzle in a bit of olive oil.
Pour the tortilla mix inside the pan and lower the heat. After 4 minutes use a large plate to cover the pan, hold it tightly and flip the tortilla onto the plate. Slide the 'non-cooked side' of the tortilla back into the pan to cook.
I recommend eating the tortilla when still a little runny in the middle. Each tortilla is different, after trying them different ways you’ll find the one you love the most - but this one is my favourite for sure.