Mix the graham cracker crumbs with melted butter until the mixture resembles wet sand. Press this mixture evenly into the bottom of your prepared baking pan to create a firm crust.
Bake the crust at 350°F (175°C) for about 8 minutes, just until it starts to set and smell toasted. Remove from the oven and let it cool slightly while you prepare the chocolate layer.
Place the chocolate chips in a microwave-safe bowl and melt in 30-second bursts, stirring after each, until smooth and glossy. Spread the melted chocolate evenly over the cooled crust.
Toast the marshmallows over a flame or under a broiler until golden brown and caramelized, then quickly layer them over the melted chocolate, pressing gently to adhere.
Use a kitchen torch to toast the marshmallows further, if desired, for an extra smoky flavor and caramelized look. Alternatively, place the bars under the broiler for a minute, watching carefully to prevent burning.
Allow the bars to cool at room temperature for about 15 minutes, then transfer to the fridge and chill for at least 2 hours or until the marshmallows and chocolate are firm and set.
Once chilled, cut into squares with a sharp knife. Serve immediately and enjoy the sticky, smoky, and crunchy layers of these irresistible s'mores bars.
