In the bowl of a stand mixer, cream together the butter, dark brown sugar, and granulated sugar until creamy and smooth, 2 minutes. Add in the egg, followed by the egg yolk, and the vanilla, mixing well after each addition. Lastly, add in the salt, baking soda, cornstarch, flour, and 1/2 cup of ground graham cracker crumbs and mix until combined. Stir in 1 cup of the chocolate chips and 1 cup of the miniature dehydrated marshmallows and mix until incorporated. Cover and refrigerate for 2 hours, up to 24 hours; this is mandatory!