Preheat the oven to 350°F. Line a baking sheet with parchment paper.
If you haven't already done so, break the graham crackers into chunks and pieces. Chop the chocolate bar into small pieces. Set the graham crackers and chocolate aside along with the chocolate chips and mini marshmallows.
In a large mixing bowl, combine the mostly melted butter, maple sugar, egg, cassava flour, baking soda, cream of tartar, and vanilla extract. Stir until a smooth cookie dough forms.
Fold in 2/3 of the crumbled graham pieces and the chocolate chips. Using a cookie scoop or a tablespoon, place scoops of the dough onto the cookie sheet. These cookie will spread out, so leave at least 2" between each cookie.
Press some more graham cracker pieces into the top of each cookie dough ball, flattening the ball slightly. Add some of the chopped chocolate bar or chocolate chips and 4-5 mini marshmallows per cookie.
Bake for 8-10 minutes. The edges of the cookies should be lightly browned. As soon as the cookies come out of the oven, add more toppings if desired.
Cool for 5-7 minutes before moving the cookies to a cooling rack to finish cooling. Store in an airtight container at room temperature or freeze for later.