Preheat your oven to 350 degrees Fahrenheit. Line a 9 by 13 inch baking dish with parchment paper. I cut one piece of parchment paper that is the width of the pan, but is long enough that it will fall over both ends. I cut a second piece that is the length of the pan, but is wide enough to fall over both sides. This allows the bars to just be lifted out of the pan after baking and cooling. (See step by step instructions below the recipe card.) In a large bowl, whisk together the flour, baking soda, baking powder, and salt.
3 cups all-purpose flour, 3/4 teaspoon baking soda, 3/4 teaspoon baking powder, 1/4 teaspoon salt
In the bowl of a stand mixer fitted with a paddle attachment or in a large bowl with a hand mixer, beat together the butter, brown sugar, and granulated sugar until light and fluffy, about 3 to 6 minutes. Add in the egg and egg yolk, one at a time. Then beat in the vanilla until just combined. Scrape down the sides of the mixing bowl and give it one final mix.
3/4 cup butter, 1 cup brown sugar, 1/2 cup granulated sugar, 2 eggs, 1 egg yolk, 2 teaspoons vanilla extract
Add the flour mixture. Turn on the mixer on low, and beat until the flour just begins to incorporate. Then turn the mixer up high for just a few seconds until the flour is fully incorporated. This will allow you to combine the flour all at once without overmixing the dough.
Stir in the chocolate chips by hand with a spatula.
1 cup chocolate chips
Press the dough into the prepared baking dish. If desired, press extra chocolate chips into the top of the bars. Bake for 20 to 22 minutes or until the edges of the cookies begin to turn golden brown.
Allow the bars to fully cool before lifting them out of the baking dish and cutting into equal pieces. Transfer to an airtight container. These are best when eaten within the first week, but will last up to 2 weeks.