Gather all your ingredients. Preheat your oven to 350°F (175°C) and line a 9x13-inch baking dish with parchment paper, leaving some overhang.
In a medium saucepan, melt the unsalted butter over medium heat. Cook, stirring frequently, until golden brown and nutty, about 5-7 minutes. Let cool slightly.
In a large mixing bowl, combine the brown sugar and browned butter. Mix until well blended. Add the lightly beaten eggs and vanilla extract, stirring until fully incorporated.
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add to the wet ingredients, stirring until just combined.
Gently fold in the milk chocolate and dark chocolate chips using a spatula.
Pour the batter into the prepared baking dish, spreading it evenly. Bake for 25-30 minutes, until the edges are golden and a toothpick comes out with a few moist crumbs.
Let the bars cool in the pan for about 10 minutes. Sprinkle with Maldon flaked salt before serving.
Using the parchment overhang, lift the bars out of the pan, slice into squares, and serve warm or at room temperature.
