Combine the graham cracker crumbs with melted butter in a bowl, mixing until the crumbs are evenly coated and hold together when pressed.
Press the graham cracker mixture firmly into the bottom of a greased 9x13-inch baking dish, creating an even crust. Chill in the refrigerator for about 10 minutes to set.
In a microwave-safe bowl or using a double boiler, melt the chocolate chips until smooth and glossy, stirring occasionally.
Evenly spread the melted chocolate over the chilled crust, smoothing the top with a spatula.
Pour the marshmallows into a microwave-safe bowl and microwave in 30-second intervals, stirring each time, until puffed and soft.
Spread the marshmallows evenly over the chocolate layer, pressing down gently to help them stick.
Place the dish under the broiler for 1-2 minutes, watching closely until the marshmallows puff up and turn golden brown.
Remove the dish from the oven and let it cool at room temperature for about 15 minutes, allowing the marshmallow topping to set slightly.
Refrigerate the bars for at least 2 hours or until fully chilled and firm before cutting into squares.
Use a sharp knife to cut into squares, serving once fully set and slightly gooey.
Enjoy these rich, sticky, and crunchy bars as a decadent treat or dessert!
