Preheat the oven to 350F and melt the butter. Make the graham cracker crumbs by adding them to a food processor and processing for 30 seconds or until crumbly.
In a large mixing bowl add the gluten-free flour, brown sugar, salt, and graham cracker crumbers. Mix together until combined.
Add in the egg, melted butter, and vanilla extract. Mix together until it becomes a dough.
Coat an 8x8 or 9x9 baking dish and add 3/4 of the dough to the bottom (save the rest for the topping). Press the dough down until there is an even layer. Bake on 350F for 10 minutes.
Remove the dough and add the chocolate chips over the top of the dough. Next, add the marshmallows over the chocolate. Finally, add the rest of the dough over the top of the marshmallow.
Place bake in the 350F oven for 15-17 minutes until bubbly and lightly browned.
Allow to completely cool for at least 30 minutes to an hour. They will be very hard and crumbly to cut if the bars are still warm. Allow them to cool completely.