• Preheat oven to 350ºF. While preheating, be sure to read tips & tricks in post above for recipe sucess.
• Place graham crackers (8 sqaures) 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 ½ cup. Set aside 1 tablespoon of crumbs for decorating later, then set bag of crumbs aside.
• Warm the unsalted butter (½ cup, i.e. 1 stick) in a microwave-safe bowl or saucepan until it’s just melted.
• In a large mixing bowl, combine the unsalted butter with the light brown sugar (½ cup) and granulated sugar (¼ cup). Stir until combined. (I recommend mixing this by hand rather than a mixer.)
• Stir in the egg (1 large) and vanilla extract (1 ½ teaspoons), followed by the baking soda (½ teaspoon), baking powder (¼ teaspoon), and salt (¼ teaspoon).
• Mix in crushed graham cracker crumbs (½ cup) and all-purpose flour (1 ¼ cups), followed by the semi-sweet chocolate chips (1 cup) and mini marshmallows (1 cup). Mix the dough until well-combined.
• 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.
• 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.
• 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:

• Beat the softened unsalted butter (½ cup, i.e., 1 stick), vanilla extract (2 teaspoons), and salt (¼ teaspoon) on medium-high speed for 1 minute until smooth. Turn the mixer to low speed then slowly add the unsweetened cocoa powder (½ cup) and powdered sugar (2 cups). You may need to stop and scrape down the sides. One tablespoon at a time, add milk (2-3 tablespoons 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 1 ½ cups frosting.