Use a mini food processor to grind the graham crackers into a powder. Or crush in a plastic bag with a rolling pan.
Gather the ingredients and equipment. In a medium bowl, use a whisk to combine the flour, baking powder, baking soda, cornstarch, salt and ground graham crackers. Set aside.
In a large with an electric mixer, mix the butter, brown and white sugar until smooth but not creamed.
Add the eggs one at a time, then the vanilla and mix until just combined. Stir in the chocolate chunks and mini marshmallow bits. With your hands, crush the 3 full sized graham crackers and stir to combine.
Use a #16 cookie scoop to make 3 oz size cookie dough balls. Place in a large container or on the baking pans. Feel free to top each cookie dough ball with 2-3 chocolate chunks.
Cover with plastic wrap and refrigerate for at least 2 hours or overnight. After 2 hours you can bake or freeze to bake at a later date.
When ready to bake, preheat the oven to 350℉ and place the cookies on a baking sheet allowing space between for them to spread (4 to a baking sheet). Bake for 13-15 minutes until slightly golden brown.
Adjust baking time depending on the temperature of the dough, less time for room temp or more time if frozen. Once baked, allow to rest on the pan for at least 10 minutes.