Preheat the oven to 350°F (180°C). Line a 9x13-inch baking pan with parchment paper or foil, making sure to leave some overhang for easy removal, and set aside.
In a large mixing bowl, whisk together the melted butter and brown sugar until fully combined, then whisk in the eggs, egg yolk, and vanilla extract until just combined.
Add the flour, baking soda, and salt and mix until just combined, then fold in the semi-sweet chocolate chips.
Scoop the batter into the prepared baking pan and spread it out into one even layer.
Bake for about 25 minutes or until the tops of the bars are set and lightly browned.
Remove from the oven and transfer to a wire rack to cool completely. Once cooled, lift the bars out of the pan using the overhang from the foil or parchment paper, slice into bars, serve, and enjoy!
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Notes
Storage Instructions: These bar cookies should be kept in an airtight container at room temperature and will last about 5 days.Freezing Instructions: You can also slice and freeze these bars for up to 3 months in a freezer bag. When ready to eat, place on the counter to thaw or gently warm in the microwave. Butter: If you only have salted butter on hand, reduce the salt in this recipe to 1/2 teaspoon.Chocolate Chips: You can add up to 12 ounces (1 1/2 cups) of mix-ins total. Instead of chocolate chips, you could experiment with butterscotch chips, peanut butter chips, chopped nuts, dried fruit, etc.