Brown the butter: Cut the butter into tablespoon-sized pieces and melt in a light-colored saucepan over medium heat. Swirl the pan constantly as the butter foams, crackles, and eventually turns golden amber with dark flecks on the bottom and a nutty aroma — about 5-7 minutes. A light-colored pan is essential so you can see the color change. Pour immediately into a large heatproof mixing bowl to stop the cooking. Make sure you scrape every last brown bit from the bottom of the pan — that is concentrated flavor.

Add the miso: While the brown butter is still hot, add the white miso paste and whisk until completely dissolved and smooth. The residual heat melts the miso right into the fat. Let the mixture cool for 10 minutes until warm but not hot — hot butter will scramble the eggs.

Add both sugars to the brown butter miso mixture and whisk vigorously for about 60 seconds until combined and slightly thickened. Add the eggs one at a time, whisking well after each. Add the vanilla and whisk for another 30 seconds until the mixture looks glossy and slightly ribbony.

In a separate bowl, whisk together the flour, baking soda, cornstarch, and kosher salt. The cornstarch is the secret to extra-thick, chewy centers — it inhibits gluten development and keeps the interior soft.

Add the dry ingredients to the wet ingredients and fold with a spatula until just combined — you should still see a few streaks of flour. Do not overmix or the cookies will be tough. Add the chopped dark chocolate and fold until evenly distributed.

The move that changes everything: Cover the bowl tightly with plastic wrap and refrigerate the dough for at least 2 hours, or up to 72 hours. Resting does three things — it hydrates the flour for chewier texture, concentrates the flavors as the brown butter and miso meld, and allows the sugars to dissolve for more even caramelization. The cookies get noticeably better at 24 and 48 hours.

When ready to bake, preheat oven to 375°F and line sheet pans with parchment paper. Scoop dough into 3-tablespoon balls — about the size of a golf ball. Place 3 inches apart on the sheet pan. Do not flatten them.

Bake for 10-12 minutes until the edges are golden brown and set but the centers still look slightly underdone and puffy. They will firm up as they cool. If they look perfectly done in the oven, they are overbaked.

Immediately press a few extra chocolate chunks into the tops of each cookie while they are still hot — this is the bakery move for those photogenic chocolate pools on the surface. Sprinkle each cookie generously with flaky sea salt. Let cool on the pan for 5 minutes, then transfer to a wire rack. The salt is not optional — it is what makes these cookies unforgettable.