Fluffy texture in a Spanish tortilla

If you want it fluffy, you'll need air. The easiest way to accomplish this is to crack the eggs in a bowl, whip them (with a whisk or a fork) for a couple of minutes. If you have a homogeneous-ish substance, add them to the onions and potatoes in your pan.

It sounds like you are over-cooking it a bit, so it is drying out. Eggs should always err on the side of undercooking for best results (with the usual precautions re. food poisoning for vulnerable groups).

Spanish Tortilla, as learned from my ex mother in law from Spain: olive oil hot in pan, cubed potato and chopped onion, salt and pepper, cover and cook on medium heat until tender stirring occasionally. Whisk until smooth 8-10 eggs with a dash of milk and pour in circular motion from middle out to edge of pan. As edges cook, with spatula, lift edges in all four directions and while tilting pan, allow egg mixture to seep under the cooked edges. Continue this until the top has little raw egg left and swirl the pan some to prevent sticking and allow "new" egg to redistribute under cooked egg . Gently press center and any bubbles as they appear. With a large plate inverted over pan, carefully flip tortilla and then slide back into pan to finish cooking. Serve with crusty bread.

Jamie Oliver has said that OLDER eggs whip up the best egg whites without having to use cream of tartar. He's right as I have done this with meringues so I don't think the age of the egg makes a difference. If anything, having your eggs near room temperature might help.

The recipe most used here is to fry the potatoes and onion, with some salt, on medium heat (you don't want them to be crispy fried, you want them soft), and on a bowl whisk the eggs well. In this point you can add a bit of milk to the eggs (softer texture) or alternatively a bit of beer (I think this is the best option).

Then add the potatoes and the onion to the bowl to mix everything well, add a bit more of salt if needed, then go back to the pan, this time with not too much oil, as little as needed to make sure the mix doesn't stick. Use medium-low heat. After a few minutes, when it doesn't stick to the sides of the pan, flip it around with the help of a dish or a cutting board, then cook on the other side and it's done ;).

As the way of flipping it with a dish and to give it the proper shape is a bit tricky, maybe this video helps:

http://www.youtube.com/watch?v=TeLsT4gZH5I&feature=related

It's in Spanish, but the flipping-shapping technique can be seen starting from 2:35.

Hope it helps :)

Put a lid on it!

Add you whisked eggs and put a lid on the pan. It doesn't have to be a perfect fit, but you need hot steam to build up above the eggs

I tend to find you can cook hotter and quicker with the lid on, but this tends to vary on pan type and how even the heat source is

When done put under the grill as per recipe