Preheat your oven to 350°F (175°C). In a mixing bowl, combine the graham cracker crumbs with the melted butter until the mixture resembles wet sand. Press this mixture firmly into the bottom of a buttered 9x13-inch baking pan to form an even crust. Bake for 8-10 minutes until slightly set and fragrant.
Remove the crust from the oven and sprinkle the chocolate chips evenly over the warm crust. The residual heat will help the chocolate melt into a gooey layer. Spread the mini marshmallows over the melted chocolate, ensuring good coverage but leaving a small border around the edges.
Bake the assembled bars for 10-12 minutes, or until the marshmallows are golden and puffed, and the chocolate is bubbling. Keep a close eye to prevent burning; the marshmallows should be lightly toasted on top.
Once out of the oven, sprinkle a pinch of salt over the marshmallow topping for enhanced flavor. Let the bars cool for about 10 minutes; this helps the marshmallow set slightly and makes slicing easier.
Use a sharp serrated knife to carefully cut the bars into squares. The marshmallow will be sticky and gooey, so gentle sawing helps create clean edges without tearing the layers.
Serve the S'mores Bars warm or at room temperature, ideally with a napkin nearby because of their sticky, melty topping. Enjoy the crispy crust combined with the soft, marshmallowy and chocolatey layers for a perfect treat.
