Preheat oven to 350°F. Line a baking sheet pan with parchment paper or a silicone baking mat.
Combine melted butter, light brown sugar and granulated sugar in a mixing bowl. Stir until combined and smooth.
Add egg and vanilla extract and mix well until smooth.
Add graham cracker crumbs, all-purpose flour, baking soda, and salt. Mix until the dry ingredients are well combined and the mixture forms a dough.
Pour in chocolate chips and dehydrated marshmallows and mix until the chocolate chips are dispersed throughout the cookie dough.
Portion the dough into balls using a large cookie scoop (3 tbsp). Place the cookie dough balls onto the prepared baking sheet pan. Allow room for spreading.
Bake the cookies for 10 to 12 minutes. The cookies will appear underdone. Remove the pan from the oven and allow the cookies to cool on the pan for 2 minutes. Transfer the cookies to a wire rack to cool to room temperature.