Bar Eme in Bilbao has been serving sandwiches with a spicy sauce for 74 years. The recipe is not kept under lock and key, but almost.

“We don't have it in any safe nor does any notary have it, we keep it in the family, it's in our heads, and none of us tells it to anyone under penalty of death,” jokes the owner. The sandwich is made with a spongy crumb bread, kneaded daily in the bar's oven, filled with artisanal York ham.