Preheat oven to 325°F. Adjust oven rack to middle lower position. Line a 13x9 inch pan with foil, letting some excess hang over the sides to make the bars easier to remove. Spray with nonstick cooking spray.
In a large bowl whisk the butter, brown sugar and granulated sugar until well combined. Mix in the egg, egg yolk, and vanilla.
In a medium bowl whisk the flour, salt, and baking soda.
Using a rubber spatula, mix the dry ingredients in. After a few stirs, (there should be lots of flour still visible), add the chocolate chips. Fold the chocolate chips until combined. Don’t overmix!
Press the batter into the prepared pan.
Bake for 23-26 minutes or until the bars are lightly golden brown on the edges, slightly firm to the touch, and the edges are slightly pulling away from the sides of the pan.
Remove from the oven and let cool on a wire rack until room temperature. Remove the bars using the overhanging foil. Transfer to a cutting board and cut into squares.
Tips: you can use chocolate chunks, butterscotch chips, white chocolate chips. You can also flavor the dough with 1 cup of nuts or raisins.