Only a crazy Latin/French recluse would call it expresso.
It is a very valid point and you almost had me accepting either spelling. But I'm more inclined to stick to the "S" as language does change in spelling and meaning and new things need adopting.
Yes Agreed . I am with the Italians and they can spell it however they want as it was their baby after all. I was just retrospectively covering my tracks for my mistake which turned out to perhaps not be a mistake depending on your point of view !