Place the butter in a light-colored saucepan over medium heat.

Let the butter melt, then continue cooking until it foams and the milk solids turn amber brown and smell toasted and nutty.

Swirl the pan often while the butter cooks.

Remove the pan from the heat as soon as the butter is browned.

Pour the browned butter, including all the brown bits, into a heat-safe bowl right away.

Let the browned butter cool for 20 to 25 minutes, until it is warm and fluid but not hot.

Whisk the cooled brown butter, brown sugar, and granulated sugar together until smooth.

Add the eggs and vanilla extract.

Whisk until the mixture is glossy and fully combined.

In a separate bowl, whisk together the flour, baking soda, fine sea salt, and baking powder.

Fold the dry ingredients into the wet ingredients just until no dry streaks remain.

Stir in the semisweet chocolate chips and chopped dark chocolate.

Cover the bowl and chill the dough for 30 to 45 minutes.

Preheat the oven to 350°F.

Line baking sheets with parchment paper.

Scoop the dough into 3-tablespoon portions.

Place the dough portions on the prepared baking sheets with room between each scoop.

Press a few extra chocolate pieces on top if desired.

Sprinkle with flaky sea salt if desired.

Bake for 11 to 13 minutes, until the edges are set and the centers still look slightly underdone.

Let the cookies rest on the baking sheet for 5 minutes.

Transfer the cookies to a wire rack to cool.