Preheat oven to 350°F (175°C). Grease a mini muffin tin. In a bowl, mix graham cracker crumbs, flour, baking soda, and salt. In another bowl, beat butter, brown sugar, and granulated sugar until light and fluffy. Add egg and vanilla extract to the butter mixture and mix well. Gradually add dry ingredients to the wet mixture and combine until a dough forms. Roll dough into 1-inch balls and place into the greased muffin tin, pressing slightly to form a cup shape. Bake for 8–10 minutes or until golden brown. Remove from oven and immediately press half a marshmallow into each cookie cup. Return to oven and bake for an additional 2–3 minutes until marshmallows are puffy. Remove from oven and top each with a piece of chocolate while still warm. Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.