Feeds 8 as a nibbly type thing and 4 as a decent lunch with some salad. Peel and slice (£1 coin thickness) 3 large potatoes and 3 white onions. Take a large non-stick frying pan and gently fry them, in a very generous glug of olive oil for as long as it takes for the onions to soften and the potato to lose it's crunch, but not soft and broken up. If you're adding any extra veg (I added a handful of slice asparagus spears) do it near the end of this cooking period. In a large bowl, beat 5 eggs and season really well. Now add the contents of the frying pan to the eggs using a slotted spoon to avoid excess oil going in. Combine well, but gently. Get the frying pan back on the heat and pour it all back in, wiggling the pan a bit for the first minute to distribute evenly. let this cook for about 7 minutes, being careful not to burn the base (keep sniffing, you'll smell it if it burns!). When it is starting to firm up nicely, you need to cook the top. You can either be brave and cover the pan with a large plate/chopping board, flip it over and very carefully slide back into the pan, or you can be a wuss like I normally am and stick it under the grill for 5 minutes. I am scarred by previous attempts using a very non-non-stick pan. Potatoes, eggs and onions everywhere. Waaaah.
The only rule is that you should have hot sauce with this, it's just soooo good. Um, that's my rule, not Spain's, just so you know. Other than that, cut into wedges, or if you want to be fancy pants traditional, little diamond shapes.