Preheat oven to 350°F.

For the cookie base:

Melt butter in a microwave safe bowl until liquefied. Using a sturdy spatula, stir in both sugars and vanilla extract. Add in eggs and stir until well combined.

In a separate bowl combine flour, baking powder and salt.

Stir flour mixture into the wet ingredients and stir until no dry spots remain.

Spoon cookie dough into a greased 9×13″ baking pan and spread into an even layer.

Bake for 20 minutes or until a toothpick inserted into the middle comes out with only a few moist crumbs. Remove pan from oven and top with about 32 large marshmallow, or however many you can fit over the top.

Return cookie bars to the oven and bake for an additional 5 minutes or until the marshmallows are puffy and melted. Remove pan from the oven and let cookie bars cool completely.

For the chocolate topping:

In a microwave safe bowl, combine chocolate chips and butter. Begin to melt in the microwave in 30 second intervals, stirring between each additional 30 second heating. Continue heating until all the chocolate has melted, but watch it carefully as the chocolate can easily burn. Once the chocolate is melted, stir in the milk.

Spread chocolate mixture over the cooled cookie bars. Top with graham cracker crumbs if desired. Allow the chocolate to set before slicing into squares.