• Preheat the oven to 350 degrees Fahrenheit and line an 11 x 7 x 2-inch baking pan with parchment paper, leaving a 1-inch overhang on both sides for easy removal of the bars. Spray the parchment paper lightly with nonstick cooking spray and set aside.

Cookie Layer

• Add ¾ cup softened unsalted butter, ¾ cup lightly packed brown sugar, and ⅔ cup granulated sugar to a large bowl and beat with a hand mixer or stand mixer fitted with the paddle attachment until light and fluffy, about 3-4 minutes.
• Add 1 large egg , 1 egg yolk, and 1 teaspoon vanilla extract and beat until fully combined, scraping down the sides and bottom of the bowl as needed.
• Whisk together 2 cups all-purpose flour, 1 ½ teaspoon cornstarch, ½ teaspoon baking powder, and ¾ teaspoon salt in a medium bowl.
• Gradually mix the flour mixture into the sugar mixture until completely combined. Stir in 1 cup chocolate chips by hand.
• Press about half of the cookie dough evenly into the bottom of the prepared pan. Set the remaining cookie dough aside and prepare the cheesecake filling.

Cheesecake Layer

• Add 3 (8-ounce) packages softened cream cheese, ⅔ cup granulated sugar, and ¾ teaspoon vanilla extract to a large bowl and beat with a hand mixer or stand mixer fitted with the paddle attachment until fully combined and smooth, scraping down the sides and bottom of the bowl as needed to ensure there are no chunks of cream cheese remaining.
• Beat ⅓ cup sour cream in on low speed until combined, followed by 2 large eggs one at a time.
• Pour the cheesecake layer over the first cookie dough layer and spread it out evenly.
• Crumble the remaining cookie dough over the top as evenly as you can. It will not fully cover it, but the cookie will spread as it bakes.
• Bake for 30-35 minutes or until the cookie layer is beginning to turn golden brown around the edges are fully set.
• Allow the bars to cool to room temperature before covering and chilling in the refrigerator for at least 6 hours before serving. Remove the bars from the pan before cutting and serving.