Place the butter in a non-stick pan and melt it on medium-low heat. Keep stirring for a few minutes until the butter starts to look brown and develops a caramel-y nutty aroma

Turn the heat all the way to the lowest setting, and add the sugars. Whisk on the lowest setting for 1-2 minutes to start dissolving the sugars

Remove from heat and cool the mixture for 5-10 minutes. It should be warm, but not hot anymore

Add the egg and yolk, and quickly whisk to incorporate. Whisk for 1-2 minutes until the mixture becomes light and smooth

Add all the dry ingredients and fold with a rubber spatula until the flour is almost mixed in

Lastly, fold in the chopped chocolate. Stop folding as soon as you don't see any unmixed flour and the chocolate is evenly dispersed

Use a 2" scoop to divide the dough into 8 ~80g balls. Don't apply pressure onto the balls, just gently pull them together

Optional: Add a few chocolate chunks to the top of the balls

Refrigerate for at least 30 minutes, but ideally 2 hours or longer

Pre-heat oven to 375F (conventional) and prepare a large cookie sheet with parchment paper

Transfer the balls to the sheet, keeping at least 3" between the balls

Bake for 10-12 minutes depending on how soft and gooey you want the cookies to be