Preheat your oven to 350 degrees Fahrenheit and move your oven rack up one level above the middle of the oven.
Cream the butter and sugars together in a large bowl using your stand mixer or a hand-held mixer on high speed. Beat in the egg, the vanilla extract and the milk.
In a separate bowl, whisk together the cocoa powder, the flour, the baking soda and the salt and when it's combined add it to the butter mixture.
Mix everything together until it's well combined and there are no streaks of flour remaining.
Mix the chocolate chips and mini-marshmallows into the dough by hand using a wooden spoon or spatula and drop the dough onto your prepared baking sheets by the tablespoonful.
Press 2-3 mini marshmallows into the top of each mound of dough and sprinkle on a little bit of the graham cracker crumbs.
Bake one tray at a time at 350 degrees Fahrenheit for 13-15 minutes or until the cookies lose their shine and the marshmallows appear toasted on top. Don't forget to move your oven rack up one position for baking...this will give the marshmallows on top of the cookies that beautiful toasted appearance. But watch them carefully! Just like when you're roasting marshmallows over the campfire, you don't want them to burn!
Let the cookies sit on the pan for 5-10 minutes after you remove them from the oven just so they cool enough to stay together.
Move them to a cooling rack to cool completely, or enjoy them warm off the pan for that perfect, ooey gooey campfire s'mores experience whenever you please!!