As a non-native english speaker my search for recipes has lead me wondering what the hell is a “spanish onion” as some recipes call for. my understanding from googling is that it is a special variety of the basic yellow onion kind of like varieties like san marzano are for tomatoes or just another name for the ‘basic yellow onion.’
Yes, a yellow onion and a Spanish onion are interchangeable. Are they the same thing? Unsure, but they are used as the same thing here in the states.