Step 1

Adjust oven rack to lower-middle position. Preheat oven to 325° F. Lightly spray a 9" x 13" metal baking pan with non-stick spray. Or, if you want really clean cuts, line the pan with heavy duty foil, letting the excess hang over the edges on the long sides of the pan. Then lightly spray the foil-lined pan with non-stick spray. This will allow you to pull up on the foil and lift the bars out of the pan.

Step 2

In a medium bowl, whisk together flour, salt, and baking soda; set aside.

Step 3

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 over mix.

Step 4

Transfer dough to prepared pan. Dough will be very thick. Press evenly into pan using a spatula and/or your fingertips. (Tip: Dough mixture can be sticky. Use the buttery side of the butter wrapper to press the dough into the pan - or simply rub your finger tips with 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. It's also fun to sprinkle M&M's over the top - the mini M&M's are our first choice!

Step 5

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. If desired, sprinkle some flaky sea salt over the top right after the pan comes out of the oven - YUM! Cool to room temperature and then cut into pieces. If using a foil lining, first cut around the perimeter of the 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.