Preheat oven to 350℉. Line a 9x9 square pan with parchment paper and set aside.
In a medium bowl, whisk together flour, cornstarch salt, and baking soda. Set aside. 2 ¼ cups (270 g) all-purpose flour 2 teaspoons cornstarch ½ teaspoon salt 1 teaspoon baking soda
In a large bowl, whisk together the melted butter and sugars together until combined and no brown sugar lumps remains. 12 tablespoons (1 1/2 sticks) unsalted butter 1 cup (213 g ) packed light brown sugar 1/2 cup (99 g) granulated sugar
Add the egg, egg yolk, and vanilla extract and mix until smooth. 1 large egg 1 large egg yolk 2 teaspoons vanilla extract
Add in the dry ingredients and stir with a wooden spoon or spatula just until combined. Stir in the chocolate chips. 2 cups (12 ounces, 340 g) semi-sweet chocolate chips
Divide the cookie dough in half. Press half of the cookie dough into the prepared pan, smoothing the top with the spatula. Pour the caramel over the cookie dough and spread out into an even layer. Drop spoonfuls of cookie dough over the caramel and spread dough with a spatula until the caramel is almost covered. Some of the caramel may still be showing. That's ok! ¾ cup salted caramel sauce
Bake cookie bars for 30 minutes or until the top of the bars are light golden brown and the edges start to pull away from the pan. Cool bars on a wire rack to room temperature. Cut bars into squares and serve.