Mix the butter and mayo together into a smooth, uniform spread with no lumps. Spread evenly on one side of each slice of bread.
Heat a medium pan over medium heat. Put both bread slices, butter-side down, into the pan. Lay one slice of cheese on each slice of bread.
Cut 3 very thin slices of the apple and lay the slices on one slice of bread to cover the whole open face of the sandwich. Lay the cooked bacon on top of the apples, and top with the syrup.
With a spatula, flip the piece of bread with just cheese over onto the other piece that is loaded with the bacon, apples and syrup, and press down on the sandwich. Cook until golden brown; flip the sandwich and cook the other side to the same color. Press down on the sandwich if necessary to bind the cheese with the ingredients, and to ensure that the cheese is melting.
Slice the sandwich in half and serve.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.