12 T. unsalted butter, gently melted and then cooled to room temperature
1 c. packed light brown sugar
1/2 c. sugar
1 large egg
1 large egg yolk
2 tsp. pure vanilla extract
2 c. semi-sweet chocolate chips, plus a bit more for sprinkling over the top of the dough (my favorite chocolate chips)
Adjust oven rack to lower-middle position. Preheat oven to 325° F. Line a 9" x 13" baking pan with heavy duty foil, letting the excess hang over the edges of the pan on the long sides of the pan. Lightly spray the foil-lined pan with non-stick spray. This will allow you to lift the bars out of the pan, for clean cuts. If clean cuts aren't a concern, just spray the interior of the pan lightly with non-stick spray and eliminate the foil lining.
In a medium bowl, whisk together flour, salt, and baking soda; set aside.
In a large bowl, whisk together melted butter, brown sugar, and sugar until combined. Add egg, egg yolk, and vanilla, and whisk until well combined. With a rubber spatula, fold dry ingredients into the wet mixture. When about half-way combined, add chocolate chips and continue to fold until just combined. Do not overmix.
Transfer mixture to prepared pan. This will be very thick. Press evenly into pan using the spatula and/or your fingertips. (Tip: Dough mixture can be sticky. I rub my finger tips in a little butter, and then press the dough into the pan.) If desired, sprinkle a few more chocolate chips over the top, pressing them in a bit.
Bake for about 23 minutes or so, or until top is light golden brown and slightly firm to the touch. For the chewiest bars, do not over bake. I might even recommend to slightly under bake! Remove pan to wire rack to cool to room temperature. Cut around perimeter of pan to loosen, and then lift bars from pan using the foil overhangs. Transfer to cutting board and cut into squares with a knife or rigid pastry cutter.