Preheat your oven to 350°F.
In a large mixing bowl, combine the graham cracker crumbs, cocoa powder, granulated sugar, melted butter, and vanilla extract. Mix until well combined and crumbly.
Press half of the mixture into the bottom of a greased 9x9-inch baking dish to form a crust. Bake for 10 minutes, then remove from the oven.
Sprinkle the mini marshmallows evenly over the baked crust, followed by the semi-sweet chocolate chips and the broken milk chocolate bars.
Top with the remaining graham cracker mixture, pressing it down gently to create a top layer.
Return to the oven and bake for an additional 15 minutes, or until the marshmallows are golden and the chocolate is melted.
Allow to cool for about 10 minutes before slicing into squares. Serve warm for the best gooey experience.