Food Tortilla Espanola; the onion prevails.

Ooh.... so my wife has gone all ninja over the last few years about her tortilla - recipe from an old Spanish great-grandma passed down through to (eventually) our friend who passed it onto my wife. There is NO onion. i hate to think of the consequences if there were onions........ is this a regional thing?

This feels like cream-or-jam-on-your-scone-first kind of factionalism..... which I am all for....