Preheat the oven to 375°F. Mix dry ingredients together: In a large bowl, whisk together the all-purpose flour, cake flour, cornstarch, baking soda, baking powder and salt. Set aside.
Cream butter and sugars: Place the cold, cubed butter into the bowl of a stand mixer and secure the paddle attachment. Let the mixer cream the butter for about 30 seconds then add in both sugars and blend until incorporated and creamy.
Then add in the egg, egg yolk and vanilla extract. Blend until mixed. If any of the mixture gets stuck on the paddle attachment or side of the bowl use a rubber spatula to knock it off.
Turn the mixer to low speed and gradually add in the dry ingredients. I add in about ¼ cup at a time. Add in 6 graham crackers, Hershey's chocolate and chocolate chips until incorporated and then turn off the machine.
Measure out the cookies into 7, ~5 oz. portions (or smaller if you prefer). Make a well in the center of the cookie with your thumbs. Slice a marshmallow in half and fold dough over marshmallow.
Decorate cookies with reserved graham cracker pieces and chocolate chunks if desired. Bake at 375°F for 10-13 minutes or until tops are golden brown. Let cool and enjoy!
GLUTEN FREE: Replace both the All-Purpose flour and Cake flour with: Bob’s Red Mill Gluten Free 1-to-1 Baking Flour .To make homemade cake flour, you’ll need 14 Tbsp. All-purpose flour and 2 Tbsp. corn starch. Mix these together and sift them twice to get them fully mixed and aerated. This will make ~1 cup flour. You only need 3/4 cup for this recipe.