- Boil the potatoes in their skins for 15–20 minutes (depending on size) until almost cooked, but still firm. Drain and run them under a cold tap to make them easier to handle, before cutting each potato into 1⁄2cm-thick slices.
- Meanwhile, defrost the spinach, squeeze out the excess water and chop it slightly.
- Add the oil to a large non-stick frying pan and put onto a medium heat. Add the onion and cook for 2–3 minutes until soft.
- Beat the eggs with the pepper, mix in the spinach and then add the potatoes.
- Pour the egg mixture into the frying pan. Use a spatula to press the tortilla down, and to press in the sides to create an even shape.
- Once the tortilla has almost set (approx 5 minutes) invert onto a plate, then slide it back into the pan to cook the other side for 5 minutes. Reduce the heat and turn the tortilla twice more, cooking for 2–3 minutes on each side to make sure the centre is cooked.
- Slide the tortilla onto a plate and leave to cool for 10-15 minutes. Ideally, serve warm, as it tastes much better. For a packed lunch, allow to cool completely before slicing and packing.
- For this tortilla recipe (also known as Spanish omelette), you can use other vegetables instead of spinach, such as peas and red pepper. Or, try adding some herbs or garlic.