Chocolate Chip Cookie Bars

1 . Stage

Preheat your oven and prepare baking pan: Preheat your oven to 350°F. Lightly grease a 9x13-inch baking pan with baking spray and line the pan with two crossing pieces of parchment paper. This will help make removing the baked cookie easier.

2 . Stage

Combine the dry ingredients: In a large mixing bowl, whisk together the all-purpose flour, cornstarch, baking soda, kosher salt, and baking powder for 30 seconds. Set this bowl aside.

3 . Stage

Combine the butter and sugars: In a separate large bowl, add the melted and cooled butter, brown sugar, granulated sugar, and vanilla. Set your electric hand mixer, fitted with the beaters to low speed and beat for 30 seconds. After the sugars and butter are combined, increase the speed to medium-low and blend for another 30 seconds. The mixture will resemble a thick paste.

4 . Stage

Add the eggs to the butter and sugar mixture: Add the eggs and egg yolk all at once to the bowl containing the butter-sugar mixture. Beat the mixture on high for 1 minute. Stop the mixer and scrape down the sides of the bowl and the beaters with a rubber spatula. Beat the mix again, on high, for one more minute, or until the mixture looks like fluffy peanut butter.

5 . Stage

Combine the wet and dry ingredients: Add the flour mixture to the mixing bowl with the wet ingredients and blend it on low speed for 30 seconds or until the flour has been incorporated. Stop the mixer and scrape down the bowl and beaters. With the mixer on low, begin mixing the cookie dough once again, this time for 1 minute.

6 . Stage

Fold in the chocolate and nuts: Use the rubber spatula to fold the chocolate chunks and walnuts into the mixture. Once these are fully mixed-in, spread the dough into the prepared baking pan in an even layer, pressing down to expel any pockets of air in the dough.

7 . Stage

Bake and cool the cookies: Bake the cookies for 30-35 minutes, or until the center of the cookie dough feels spongy and the edges are dry and medium-brown in color. Remove the pan from the oven and allow the cookies to cool completely in the pan.

8 . Stage

Cut the cookies and serve: Once cool, carefully remove the cookies from the pan by lifting the parchment paper-liner and transfer to a cutting board. Using a sharp knife press down, rather than drag it through, to cut the cookies into your desired amount of bars. Store leftover bars in an airtight container at room temperature for up to 5 days.