I wouldn't say the contents change what it is - a sandwich is a filling between slices of bread, nothing states it must be savoury, even though they often are.

I wouldn't say the contents change what it is - a sandwich is a filling between slices of bread, nothing states it must be savoury, even though they often are. Jam, honey and (mashed) banana are also sandwich fillings. That said, there is no way it would qualify as cake, which would require a much sweeter and thicker batter - bread isn't the same.