Just AddMarmite

Toast the bread in your toaster until a very light brown, and pre-heat your grill (or broiler).Spread the mayo over one side of the toasted bread. Mix half the Marmite with the mayo, spreading it thinly on each slice. Do not overdo it with the Marmite (half a heaped teaspoon per slice is plenty). Place the sliced cheese on top of the toasted bread and place in the grill until the cheese melts and begins to lightly brown in places. Remove from the grill and cut in two before serving.