Whisk the melted butter and sugars in a large bowl until combined.
Add the egg and vanilla and mix well.
Using a rubber spatula, fold the flour, salt, and baking soda into the butter mixture until just combined; do not overmix.
Fold in the chocolate chips.
Pour the batter into the prepared pan, smoothing the top with the spatula.
Bake until the top of the bars is light golden brown, slightly firm to the touch, and edges start pulling away from sides of pan, about 15-25 minutes.
Cool on a wire rack to room temperature.
I like a good salty/sweetness to my chocolate chip cookies, so I used salted butter along with the salt. If you like your cookies on the sweeter side, use unsalted butter or cut back on the salt in these.
Butter: Just barely melting the butter helps to speed things along. It takes about 30 seconds in my microwave to melt the butter without getting it too hot.
Flour: To keep these bars soft and chewy, be sure to properly measure the flour. First, sift or stir the flour to break it up. Then lightly spoon it into the measuring cup and level. You don't want to pack the flour or the bars will be heavy and dry.
Salt: Or use 1/4 teaspoon of table salt.
Chocolate chips: Feel free to use bittersweet, dark, or milk chocolate chips if you prefer.
I recommend mixing this dough by hand. It's easy to do, and it helps to prevent overworking the dough.