According to the kids and teenagers at work (and we all know Gen Z are the experts in everything) two slices of bread make one sandwich, cut it in half and it's half a sandwich.
Anything not made with slices of bread has it's own name and therfore is not called a sandwich (ie hotdogs, burgers etc) but it is possible to have a burger sandwich.
I'm not convinced. That may work for yer homemade sandwich, or even yer shop-bought sandwich in a triangular package. But what about the buffet situation? If you put one triangular egg and cress, one cheese and pickle, and one smoked salmon and cream cheese on the same plate, and take them back to your table, how many sandwiches have you got? 1.5? No, surely you have three sandwiches. Context is everything.