Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper or foil, leaving an overhang on the sides for easy lifting. If you don't have parchment, spray well with cooking spray.

In a medium bowl, whisk together the all-purpose flour, baking soda, and salt until well combined. Set this bowl aside.

In a large mixing bowl, combine the melted and slightly cooled butter with both the brown sugar and white sugar. Stir vigorously until the mixture is smooth and creamy. Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract until fully incorporated.

Gradually add the dry flour mixture to the wet ingredients, mixing on low speed or by hand until just combined. Be careful not to overmix the dough once the flour is added; overmixing can lead to tough bars.

Fold in the chocolate chips using a spatula. You can reserve a few to sprinkle on top if you like, for an extra pretty finish.

Transfer the cookie dough to your prepared 9x13 inch baking pan. Use a spatula or your hands (lightly floured if sticky) to press the dough evenly into the bottom of the pan. Make sure it's spread from edge to edge.

Place the pan in the preheated oven. Bake for 25-35 minutes, or until the edges are golden brown and the center appears set but still looks soft and slightly underdone. Remember, the center will continue to set as it cools.

Remove the pan from the oven and place it on a wire rack to cool completely to room temperature. Resist the urge to cut into them while warm, as they will be very gooey and fall apart. Once fully cooled, use the parchment paper overhang to lift the entire slab of cookie bars out of the pan. Slice into squares and serve.