Preheat oven to 350°F (177°C). Line a baking sheet with parchment paper.

In a large bowl or a stand mixer fitted with the paddle attachment, beat your softened butter until smooth and creamy, about 1-2 minutes.

Add both your brown sugar and white granulated sugar to the beaten butter and mix until light and creamy. About 2-3 minutes.

Add your large egg and vanilla, beating it into the mix until everything is well incorporated. Set this mix aside.

In another bowl, whisk together the flour, baking soda, salt, and cornstarch.

Gradually add the dry ingredients to the sugar mixture, stirring until well combined. The batter should be thick.

Add your chocolate chips to the mixture and gently stir until JUST combined.

Using the graham crackers, marshmallow, and chocolate bar, create a s'more. Layer a graham cracker, a piece of chocolate, and then a whole marshmallow.

Using about a handful of the cookie dough (about ¼ cup), cover the s'more until you can no longer see the marshmallow and chocolate. If the marshmallow or graham cracker peeks slightly through, that is okay.

Place the cookie dough portions on a lined cookie sheet with parchment paper. Make sure to leave enough space between each cookie to allow for spreading while it bakes.

Bake for about 10-15 minutes or until the cookies are lightly golden brown around the edges. They will look super soft, and the marshmallows should look ooey-gooey. The cookies will continue to bake out of the oven, so avoid overbaking.

Carefully place a few more chocolate chips on top of the hot cookies. Sprinkle flaky sea salt all across the cookies. Allow them to cool for about 10 minutes on the cookie tray before enjoying!