On the other hand, 'sur mia sandviĉo' sounds like there's butter smeared on top of the upper piece of bread. 'In between my sandwich(es)' – now that's odd! What about 'je la s-o' or 'ĉe la s-o' – I know it's unorthodox but still... Personally, I would just say 's-o kun/sen butero'. That's what seems the most natural to me.
The Esperanto word sandviĉo seems to cover all types of sandwiches. For me the default type is what seems to be called in English open or open-face sandwich, that is one slice with some topping. In some parts of the world the word sandwich refers exclusively to layered bread, i.e. at least two slices with some filling between them. There also seems to be countries, where the word sandwich is reserved for breads with some particular fillings.
Since there is the word sur in the sentence, I'm inclined to think, that here we talk about the first alternative, the open one.
Ĉu iu scias kiel precizigi, pri kia tipo de sandviĉo temas?
I agree, though I have not heard anyone talk in English about having meat ON a sandwich.
Definition of sandwich from the Merriam Webster dictionary,
1a : two or more slices of bread or a split roll having a filling in between
b : one slice of bread covered with food Have an open-faced sandwich, with one slice of bread instead of two, mustard instead of butter, and some vegetable sticks to munch on.
Definition of Emparedado de la Real Academia Española (RAE) 2. m. Porción pequeña de jamón u otra vianda, entre dos rebanadas de pan de molde.
In Mexican Spanish as far as I know a sandwich is ALWAYS 2 slices of bread with something in the middle.
The difference between a hamburger and a sandwich (besides the ingredients in them) is that a hamburger has round buns and the sandwich square slices.
If you want to refer to 1 slice of bread then you put something on, but if you want to refer to 2 slices of bread you put something in.
pon mantequilla EN/SOBRE la rebanada de pan - put butter ON the slice of bread pon mantequilla EN/DENTRO DE el sandwich - put butter IN the sandwich
It would be interesting to know the definition of sandwich in Portuguese, French, Italian, German and the Slavic languages and how they put butter in or on or something else in their bread.