01 -
Preheat oven to 350°F. Ensure the oven is fully preheated before baking for even results.
02 -
In a large mixing bowl, whisk together graham cracker crumbs, cocoa powder, and powdered sugar until well combined and free of lumps.
03 -
Pour melted butter into the dry mixture. Stir using a sturdy spoon or spatula until evenly moistened. The mixture will be thick and sticky.
04 -
Fold in mini marshmallows, chocolate chips, and chopped nuts if using. Mix just until evenly distributed. Do not overmix to preserve marshmallow texture.
05 -
Lightly grease a 9x13 inch baking pan with non-stick spray or line with parchment paper. Spread the mixture evenly across the pan and press gently to level the surface using a spatula.
06 -
Place the pan on a middle oven rack and bake for 25 to 30 minutes, or until the edges look set and the center is slightly firm to the touch.
07 -
Remove the pan from the oven and allow to cool completely in the pan. Once cooled, cut the bars into 40 even squares with a sharp knife.