Sift together the flour, baking soda, salt, and cornstarch and set aside.
Using an electric mixer, cream together the soft butter and shortening
Mix in the granulated sugar and brown sugar until very creamy.
Add the eggs and egg yolks one at a time.
Mix in the pure vanilla.
Slowly add the dry ingredients.
Mix until all the dry ingredients have been incorporated.
Do not over mix.
Stir in the chocolate chunks, marshmallows, and graham crackers in by hand.
Use an ice cream scoop and drop cookies onto a baking sheet that has been lined with parchment paper.
Bake 375 degrees for 15 minutes if using a 1/4 cup ice cream scoop.