Preheat the oven to 350°F (175°C) to ensure even baking.

In a saucepan over medium heat, melt the salted butter until it turns golden brown and nutty—about 5-7 minutes.

Cream together the brown butter with brown sugar and granulated sugar until smooth and creamy.

Mix in the egg, egg yolk, and vanilla extract until fully incorporated.

In a separate bowl, whisk together all-purpose flour, baking powder, baking soda, and salt.

Gradually add the dry mixture to the wet mixture, mixing until just combined.

Gently fold in the chopped dark chocolate.

Use a cookie scoop to drop portions of dough onto lined baking sheets, spacing them about 2 inches apart.

Sprinkle flaky sea salt and extra chopped chocolate on top of each cookie.

Bake for 10-12 minutes, or until the edges are golden brown but the centers still look soft.

Allow the cookies to cool on the baking tray before transferring them to a wire rack.