Preheat oven to 375 F. Grease cups of a 12-cup muffin tin.
In a large bowl, stir together flour, graham cracker crumbs, baking soda and salt. Set aside.
In a medium bowl, whisk together brown sugar, egg, oil, vanilla, and buttermilk. Add to flour mixture and stir until just combined. Do not over mix.
Fold chocolate chips and marshmallows into the batter.
Divide batter between muffin cups. Bake in preheated oven 18 to 20 minutes or until a toothpick inserted near the center comes out clean.
Remove from oven and cool on wire rack. Makes 12 muffins.