In a large bowl, whisk the flour, baking soda, cornstarch, and salt together. Set aside. 2 ¼ cups (280 g) all-purpose flour 1 teaspoon baking soda 2 teaspoons cornstarch ½ teaspoon salt
In a medium bowl, whisk the melted butter, brown sugar, and granulated sugar together until smooth and combine. ¾ cup (170 g, 1 ½ sticks) unsalted butter, ¾ cup (150 g) packed light brown sugar ½ cup (100 g) granulated sugar
Whisk in the egg and egg yolk until evenly mixed in. Whisk in the vanilla extract until evenly incorporated. 1 large egg 1 egg yolk 2 teaspoons pure vanilla extract
With a spatula or wooden spoon, stir in the flour mixture and mix together. The dough will be soft and thick. Fold in the chocolate chips and Oreo pieces. 1 cup (170 g) semi-sweet chocolate chips 12 Oreo cookies
Using a small cookie scoop the dough into heaping 2 tablespoons (about 50 g). Roll into balls and place into a parchment lined baking sheet.
Cover the unbaked cookies tightly with plastic wrap and chill in the refrigerator overnight for at least 2 hours, ideally overnight. Alternately, you can chill the bowl of cookie dough and scoop the next day (just allow several minutes at room temperature to allow for easy scooping).
When ready to bake, preheat oven to 350°F (180°C). Line large baking sheets with parchment paper or silicone baking mat. Place cookie dough balls spaced a few inches apart.
Bake the cookies for 11-13 minutes or until the edges are very lightly browned. The centers will look very soft, but the cookies will continue to set as they cool. When they come out of the oven I like to press a few extra chocolate chips and a few Oreo pieces on top for appearance! Cool on the baking sheet for 10 minutes. After 10 minutes of cooling on the baking sheets, transfer cookies to a wire rack to cool completely. Cookies stay fresh covered at room temperature for up to 1 week.