In a medium saucepan over medium heat, melt the salted butter while stirring continuously. Keep an eye on it as it foams and begins to turn golden brown, which takes about 8-10 minutes.

Transfer the browned butter to a mixing bowl and allow it to cool slightly.

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

Using an electric mixer, whip the cooled brown butter until fluffy, about 2-3 minutes. Gradually add the brown sugar and granulated sugar, mixing until light and pale.

Incorporate the whole egg, egg yolk, and vanilla extract into the mixture. Beat until smooth.

Gradually fold the dry ingredients into the wet mixture using a spatula until just blended. Fold in the dark chocolate chunks.

Using a cookie scoop, portion out the dough into 16 equal balls and chill in the refrigerator for 15 minutes.

Preheat your oven to 350°F (175°C). Arrange the chilled dough balls on lined baking sheets about 2 inches apart and bake for 10-11 minutes.

Remove from the oven and shape cookies into perfect rounds while still warm. Transfer to a wire rack to cool completely and sprinkle with flaky sea salt.