Step 1

To the bowl of a stand mixer fitted with the paddle attachment, combine the butter, sugars, egg, vanilla, and beat on medium-high speed until well-creamed, light and fluffy, about 5 minutes (or use a hand mixer and beat for at least 7 minutes).

Step 2

Stop, scrape down the sides of the bowl, and add the flour, cornstarch, baking soda, optional salt, and mix until just combined, about 1 minute.

Step 3

Add the graham crackers, chocolate chips, marshmallows and beat momentarily to incorporate, less than 1 minute, or fold in by hand.

Step 4

Using a medium 2-inch cookie scoop, form heaping two tablespoon mounds (I made 26). Place mounds on a large plate, flatten mounds slightly with your palm, cover with plasticwrap, and refrigerate for at least 2 hours, or up to 5 days, before baking. Do not bake with warm dough because cookies will spread and bake thinner and flatter.

Step 5

Preheat oven to 350F, line a baking sheet with a Silpat, or spray with cooking spray. Place mounds on baking sheet, spaced at least 2 inches apart (I bake 8 cookies per sheet).

Step 6

Bake for 8 minutes, or until edges have set and tops are just beginning to set, even if slightly undercooked, pale and glossy in the center. Do not bake longer than 9 minutes if you want ooey-gooey Smores-like cookies because they firm up as they cool (The cookies shown in the photos were baked with dough that had been chilled overnight, allowed to come to room temp for 15 minutes, and were baked for 8 minutes, with trays rotated at the 4-minute mark. They have chewy edges with soft, pillowy, gooey centers).

Step 7

Allow cookies to cool on the baking sheet for about 5 minutes before removing and transferring to a rack to finish cooling.