When I was in Spain, I made 3 eggs for breakfast. There were a total of 5 yolks. How rare is this?

Double yolk eggs are fairly common...

If you're wondering what the odds of finding a double-yolker are, it's estimated to be about 1 in every 1,000 eggs in commercial settings. The rates in backyard flocks or pullet (young hen) groupings can be even higher-sometimes as much as 1 in 50.

https://www.southernliving.com/why-some-eggs-have-2-yolks-11781507

To get five yolks from three eggs, you must have two double-yolked eggs (DYE) and one regular egg. The probability of finding a single double-yolk egg varies greatly based on the age of the hen and the size of the egg.

Double-yolk eggs are almost exclusively laid by young hens whose reproductive cycles are not yet fully synchronized. The probability of finding a DYE is roughly 1 in 1,000.

Assuming a random selection from the general commercial supply (1 in 1,000 chance which is 0.1%) the probability of finding two DYE and one regular egg is a question of multiplication:
P = 0.001 x 0.001 x 0.999 = approximately 0.000001. This is one in a million.

You should have gone out to buy a lottery ticket.

You can actually purposely buy double yolk eggs...

Description

Farm fresh mixed double yolk chicken eggs. These eggs are mostly double yolks, though occasionally 1 or 2 large single-yolks eggs can get mixed in, hence the name.

https://gofflepoultry.com/shop/mixed-double-yolk-eggs/

https://www.grubstreet.com/2014/11/sauders-double-yolkers-eggs.html