Grease a 10-inch cast iron skillet. Preheat oven to 350 degrees F.
In a medium bowl cream the butter and the sugar with an electric mixer. Add all the eggs at once and mix in. Mix in the vanilla. Sift the flour and the salt together and blend in.
Spread the batter in the prepared skillet. Place in the preheated oven and bake for 25 to 30 minutes.
Remove the skillet from the oven and top the brownies with the miniature marshmallow. Place back in the oven and continue to bake about another 5 minutes or until the marshmallow begins to brown.
While the brownies are baking add the 1/4 cup of cream to a small saucepan. Heat until simmer. Remove from heat and add the milk chocolate chips. Place the cover on the saucepan and set aside. Once the chocolate chips are softened stir the mixture until well blended. Set aside
Also while the brownies are baking the graham crackers can be crushed. I do not crush them all the way I like to leave small pieces of graham crackers when I crush them.
Once the marshmallows are slightly browned remove from the oven and drizzle the ganache over top of the marshmallows. Sprinkle the crumbs over top of the ganache. Serve