Preheat oven to 350 F. Grease a 12 cup muffin tin, set aside. In a medium bowl, whisk together flour, crushed graham crackers, salt and baking soda.
In another large bowl with a mixer, beat softened butter with granulated sugar until fluffy. Add in egg and vanilla extract, beat until smooth.
Add in flour mixture in two separate additions, beating after each until all of the flour is incorporated. Evenly divide the cookie dough into the prepared muffin tin. Bake for 13-15 minutes.
Remove from oven and top each with 1/4 of the chocolate bar and mini marshmallows. Bake for another 4-5 minutes. Let cool completely.
