Preheat oven to 350F and line a baking sheet with parchment paper. Cream softened butter, brown sugar, and granulated sugar together with a hand mixture or electric mixer until smooth and fluffy.
Mix in the egg and vanilla extract. in a separate bowl combine the flour, baking soda and cinnamon. Fold dry ingredients into wet ingredients with a rubber spatula.
Mix in graham cracker pieces and chocolate chunks with the spatula.
Scoop about a 1/4 cup of batter out of the bowl for each cookie. Roll into. a ball and place on the cookie sheet with lots of space between each cookie - I recommend baking in 2 batches.
Bake at 350F for 15-16 minutes. Remove from oven and place a marshmallow sideways on top of each cookie. Bake for another 2 minutes and remove from the oven. Use a spatula to press down gently on the warm marshmallows on the cookies so they stick to the cookie.
To get a golden brown top to the marshmallow, use a torch to cool slightly OR increase the oven heat to a broil and place the cookie sheet below the broiler for 30 seconds or less! careful because the marshmallow will burn quickly
Remove the cookies from the oven and transfer to a wire rack to cool completely.
Notes
use gluten free all purpose flour and gluten free graham crackers to make these cookies gluten free
use mini marshmallows in place of full size if necessary
you can use dark chocolate chips or semi sweet chocolate chips in place of the milk chocolate