Preheat oven to 325°F and place a rack in the center position. Spray a 9×13-inch pan with cooking spray, line it with parchment paper leaving an overhang on two sides for easy removal.

Melt 12 tablespoons unsalted butter in the microwave in a microwave-safe bowl. Set the melted butter aside to cool to room temperature (hot butter will melt the sugars and make greasy bars).

In a large bowl, whisk the cooled melted butter with 1 cup light brown sugar (lightly packed) and 1/2 cup granulated sugar until smooth.

Add 1 large egg, 1 large egg yolk, 1/2 tablespoon vanilla extract, and 2 tablespoons maple syrup (optional). Whisk until the mixture is smooth and emulsified.

Using a wooden spoon, stir in 1/2 teaspoon baking soda, 3/4 teaspoon salt, and 2-1/4 cups flour until just combined. Do not overmix.

Fold in 1-1/4 cups chocolate chips. Reserve a few chocolate chips if you want to press extra on top before baking.

Transfer the dough to the prepared pan and press it into an even layer. If desired, press the reserved chocolate chips onto the top.

Bake for 23–28 minutes, until the top is no longer glossy and the edges are lightly golden. Be careful not to overbake.

If using, sprinkle flaky sea salt over the bars immediately after removing them from the oven. Let the bars cool completely in the pan, then lift them out using the parchment overhang, cut into bars, and serve.