Wait momentarily before adding the egg so you don’t scramble it. Add the egg, brown sugar, vanilla, and whisk until smooth.
4 Add the flour and stir until just combined, don’t overmix.
5 Add the graham crackers and any crumbs on cutting board, marshmallows, chocolate chips and fold to incorporate.
6 Turn batter out into prepared pan, smoothing the top lightly with a spatula.
7 Bake for about 20 to 22 minutes, or until bars have firmed up in the center and edges will be set. Some marshmallows may have developed a hint of golden color.
8 Allow bars to cool in pan for at least 30 minutes before slicing and serving.