Bakery Style S'mores Cookies

Chop your chocolate and set aside.
In a medium-sized bowl, whisk together the flour, cornstarch, baking soda, baking powder, and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, or a large bowl if using a handheld mixer, beat together the butter, brown sugar and granulated sugar on medium-high speed until combined, light and fluffy.
Add the egg, egg yolk, vanilla extract, and sour cream and beat on medium speed until combined, scraping down the bottom and sides of the bowl as necessary.
Add the dry ingredients to the wet ingredients and mix on low speed until a dough forms. Add the graham cracker pieces and chopped chocolate and fold until evenly incorporated throughout the dough.
Tightly cover the bowl and chill the dough for 2 hours. Once the two hours is up, preheat your oven to 350F and line a baking sheet with parchment paper.
Scoop the dough using a large cookie scoop (70 grams of dough per cookie or about ¼ cup). Divide the scooped dough in half and flatten both pieces into discs.
Place one half of a marshmallow on one disc, then put the other disc on top and seal the edges. Roll into a ball and place on your baking sheet.
Space the cookies 3-4 inches apart. Bake for 9-10 minutes until golden brown and the edges are set.
Let cool on the pan for 5 minutes. Transfer to a cooling rack to cool for another 10 minutes for a warm cookie, or let cool completely. Store in an airtight container at room temperature. Enjoy!