Design Eat Repeat

0 Preheat oven to 350ºF. While preheating, be sure to read tips & tricks in post above for recipe sucess.
31 Place graham crackers ([adjustable]8 sqaures[/adjustable]) in a plastic ziploc bag. Use a rolling pin or metal pan to crush the crackers until you get graham cracker crumbs. This will equal [adjustable]½ cup[/adjustable]. Set aside 1 tablespoon of crumbs for decorating later, then set bag of crumbs aside.
21 Warm the unsalted butter ([adjustable]½ cup, i.e. 1 stick[/adjustable]) in a microwave-safe bowl or saucepan until it’s just melted.
26 In a large mixing bowl, combine the unsalted butter with the light brown sugar ([adjustable]½ cup) and granulated sugar (¼ cup[/adjustable]). Stir until combined. (I recommend mixing this by hand rather than a mixer.)
22 Stir in the egg ([adjustable]1 large) and vanilla extract (1 ½ teaspoons), followed by the baking soda (½ teaspoon), baking powder (¼ teaspoon), and salt (¼ teaspoon[/adjustable]).
23 Mix in crushed graham cracker crumbs ([adjustable]½ cup) and all-purpose flour (1 ¼ cups), followed by the semi-sweet chocolate chips (1 cup) and mini marshmallows (1 cup[/adjustable]). Mix the dough until well-combined.
24 Generously grease a cookie cake pan. If you plan to invert the cake onto a tray (rather than serving in the pan), I highly recommend lining the bottom with parchment paper in order for the cookie cake to invert out of the pan easily.
25 Spread dough into an even layer in pan. Bake for 14 to 16 minutes, or until edges are slightly golden brown. Do not overbake; it might look a little under-baked, but the residual heat from the pan will continue to bake the cookie even after you take it out of the oven. Cool completely.
27 Use a piping bag and large star tip to create a simple buttercream border. Immediately after piping, top with mini marshmallows and the 1 tablespoon of reserved graham cracker crumbs.
To Make Chocolate Buttercream Frosting:
30 Beat the softened unsalted butter ([adjustable]½ cup, i.e., 1 stick), vanilla extract (2 teaspoons), and salt (¼ teaspoon[/adjustable]) on medium-high speed for 1 minute until smooth. Turn the mixer to low speed then slowly add the unsweetened cocoa powder ([adjustable]½ cup) and powdered sugar (2 cups[/adjustable]). You may need to stop and scrape down the sides. One tablespoon at a time, add milk ([adjustable]2-3 tablespoons[/adjustable] total).Beat on high for 2-3 minutes until creamy and the frosting is at a good consistency to pipe. If it looks too runny, add more powdered sugar. If it looks too stiff, add a tiny bit of milk until you get to the desired consistency. This will make just enough frosting to pipe a border along the edges. If you plan to write or decorate the center of the cake, double the recipe. Makes [adjustable]1 ½ cups[adjustable] frosting.