Preheat your oven to 325° F.
Heavily grease a 9x13 pan, or line with parchment paper.
In a large bowl, whisk together flour, baking soda and salt.
In a separate bowl, whisk together sugar, brown sugar, and melted butter until creamy. Add egg, egg yolk, and vanilla, and whisk until again until well combined. Gently fold dry ingredients into the wet mixture until just mixed.
Stir in chocolate chips and fold until just combined. Avoid overmixing.
Transfer the thick dough mixture to your baking pan. Use the back of a spatula or hands to press the dough evenly into the pan.
Bake for about 23-28 minutes, or until the top becomes a light golden brown. For a chewier version, slightly under bake.
Remove pan to a wire cooling rack. Once cooled, cut into squares for serving.
Delicious topped with whipped cream or a scoop of vanilla ice cream!