1. Slice the onion thinly and fry in a non-sticking pan with a bit of olive oil over a high heat until lightly golden brown.
2. Add the chopped chorizo and cook for a further 2 minutes and remove from the pan.
3. Mix the crisps in a bowl with the onion, chorizo, eggs and olives, and season with a pinch of black pepper. Leave the mix soaking for 10 minutes so that the crisps soak up all the egg.
4. Drizzle a bit of olive oil into the pan and pour in the egg mix. Lower the heat to a minimum. Gently cook the tortilla for a few minutes or until set on the bottom but still with some wet egg on top.
5. Finish cooking under a hot grill for about 3-5 minutes - the top should have a lightly golden colour.
6. Make the garlic mayonnaise if using: place the garlic, egg yolks, salt and a few drops of lemon juice in a blender and mix. Slowly add the oil in a thin and long drizzle until the mayonnaise has a thick creamy texture. Serve with the warm tortilla.
Our thanks to the British Egg Council for providing this recipe.