Preheat the oven to 350°F. Line a 9x9-inch baking pan with parchment paper, leaving a few inches of overhang on two sides for easy removal. Lightly grease the parchment.
In a large bowl, beat the softened butter, brown sugar, and granulated sugar with an electric mixer on medium speed for about 2 minutes until light and creamy. Add the egg and vanilla extract and beat until well combined.
In a separate bowl, whisk together the gluten free flour, graham cracker crumbs, baking powder, salt, and cinnamon. Add the dry mixture to the wet mixture and stir with a spatula until a thick, slightly crumbly dough forms.
Press about two-thirds of the dough firmly into the bottom of the prepared pan in an even layer. Scatter the chocolate chips evenly over the dough, pressing them in gently.
Take small pieces of the remaining dough and flatten them between your fingers, then lay them over the chocolate chips. It is totally fine if there are gaps - this creates a rustic, layered look and lets the chocolate peek through.
Bake for 22 to 25 minutes, until the edges are golden and the top is just set. Remove the pan from the oven and turn on the broiler to high.
Scatter the mini marshmallows evenly over the top of the bars in a single layer. Place the pan under the broiler for 60 to 90 seconds, watching constantly, until the marshmallows are puffed and deeply golden brown in spots. They go from perfect to burned very quickly, so do not walk away.
Let the bars cool completely in the pan for at least 1 hour - they need this time to firm up and set so they slice cleanly. Use the parchment overhang to lift them out, then slice into squares. Store covered at room temperature for up to 3 days.