Preheat oven to 350°F. Lightly grease or spray a 9-inch cake or pie pan with cooking spray. Melt the butter in the microwave and let cool to room temperature (combining sugars with hot butter results in greasy cookies).
In a medium bowl, use a wooden spoon to mix the melted and cooled butter, granulated sugar, and brown sugar until combined. Add egg and vanilla. Mix until combined.
In a separate bowl, stir together flour, baking soda, salt, and chocolate chips. Add dry ingredients to wet ingredients and stir until just combined. It may seem like the dough is dry and not coming together, but just keep mixing and it will.
Once you’ve got a smooth dough, add it to the prepared cake pan. Smooth the dough around the pan, making the center higher than the edges (edges tend to rise more). Bake for 20 minutes.
Remove and sprinkle the chopped graham crackers and mini marshmallows onto the cookie. Bake another 4–7 minutes or until cooked through and golden around the edges (it should still be soft and slightly underbaked in the center, about 5 minutes for me).
Remove and enjoy immediately. I like adding a few scoops of vanilla bean ice cream to the center. If it won’t all be enjoyed the same day, cut it into wedges and serve like a pie with ice cream scoops on individual slices.
Video
Notes
Note 1: Make sure to spoon and level the flour measurement. If you scoop a measuring cup into a bag of flour, you will pack in too much flour (drier cookie).Storage: Keep any leftovers at room temperature, covered tightly with plastic wrap. Piezookies that were topped with ice cream won’t store well at all. Even if the ice cream is scraped off, whatever melted into the cookie will make it soggy.