Another accepted sandwich variant is the toasted sandwich in which the bread has been put into a toaster . These differ from a normal sandwich in that they have a single slice of bread instead of two , with toppings instead of a filling . The open-faced sandwich also has a history differing from that of the true sandwich , having originated between the 6th and 16th centuries , with stale slices of bread used as plates called `` Trenchers '' ( whereas its relative , the modern sandwich , traces its roots to the Earl of Sandwich instead ) .