Instructions

• Preheat the oven to 350°F (175°C). Have a 9x13-inch baking dish ready.
• In a small bowl, whisk together the 2 cups all-purpose flour, ½ teaspoon baking soda, and ½ teaspoon salt; set aside.
• Place the 1 cup unsalted butter in a skillet over medium heat. Stir or swirl occasionally as it melts. Cook until the butter foams and the milk solids turn golden brown and small brown bits appear on the bottom of the pan, stirring as needed.
• As soon as brown bits appear, remove the skillet from the heat and continue stirring for about 30 seconds to finish browning. Allow the browned butter to cool slightly so it is warm but not scalding.
• Using a pastry brush, brush some of the browned butter over the bottom and sides of the 9x13-inch dish to grease it.
• Place the 1 1/2 cups light brown sugar (loosely packed) in a large bowl. Pour the warm browned butter into the sugar and mix with a spatula or wooden spoon until combined and smooth; the sugar will soften.
• Add the 2 lightly beaten eggs to the sugar-butter mixture one at a time, stirring after each addition so the eggs incorporate and do not cook from the remaining heat. Stir in the 1 tablespoon vanilla extract.
• Add the reserved dry ingredients to the wet ingredients and stir with a wooden spoon or spatula until the flour is almost fully incorporated; avoid overmixing.
• Stir in the 1 cup milk chocolate chips and 1 cup dark chocolate chips until they are evenly distributed through the batter.
• Press the batter evenly into the prepared 9x13-inch dish.
• Bake in the preheated oven for 25–30 minutes, or until the top is golden brown and the center is set.
• Remove the pan from the oven and immediately sprinkle the top with Maldon flaked salt.
• Let the bars cool completely in the pan on a wire rack before slicing into squares.