Now that is a strange coincidence... I just made one today and was about to suggest it.
Basically slice about 750g of potatoes (thin slices, or they won't get soft enough) and one onion, and fry them in a smallish frying pan in just under 150ml of olive oil for 15 minutes, while stirring constantly (if you think you have too many potatoes, you might want to remove some; it's what I did). Then beat five eggs and stir in the potato/onion mixture. Add plenty of salt and pepper, then leave for 15 minutes while you clean out the pan. Then add two tablespoons of olive oil to the pan, and pour in the tortilla mixture. Let this cook for 10 minutes on a low heat, then slide it off carefully onto a plate (If it sticks, try your best to loosen it: a non-stick pan might help) Put the frying pan upside down over the plate and turn everything upside down, so that the uncooked side of the tortilla is facing the pan. Cook this on the same heat for about 5 minutes. Your tortilla is now done! (took me about an hour) You can leave it to cool or eat it warm; personally I think it would be nicer warm. All the potato makes it very filling.
Edit: The recipe looks far more complicated than it actually is; I was fine, and I have very little cooking experience.