Preheat the oven to 350 degrees and either butter or line an 8 x 8-inch pan with parchment paper that overhangs the edges. Parchment is my preferred method because it's so easy to remove the bars.

In a small bowl, combine the graham cracker crumbs, sugar, and melted butter. Mix well so the crumbs are completely coated. Transfer to the prepared baking pan. With the back of a spoon or a measuring cup, gently tap to compact the crumbs into a crust.

Layer either chocolate chips or Hershey bars over the crumbs. Bake in preheated oven for 5-7 minutes or until the chocolate is melted. Remove from the oven. Using an offset spatula or butter knife, spread the melted chocolate in an even layer. Let cool until the chocolate is firm. I usually refrigerate for a few minutes to speed up the process.

Preheat the oven to broil. Layer the mini marshmallows on top of the firm chocolate in a single layer. I like to pack them tightly. More marshmallows that way :)!

Place the pan in the oven and broil until the marshmallows are toasted. This will take seconds.

Cut the bars into squares or rectangles and serve either warm, room temperature, or store them in the refrigerator.