Whisk both sugars into the bowl with brown butter.
Whisk in the egg and vanilla until well combined.
Add in the flour, baking powder, baking soda, and salt. Use a rubber spatula to fold the mixture together just until a few flour streaks remain.
Add in the chocolate and fold the mixture together just until no flour streaks remain.
Scoop out 2 tbsp. portions of the chocolate chip cookie dough. Then, remove the brownie cookie dough from the fridge and scoop out 1.5 tbsp. scoops of that dough.
Use a knife or your hands to split each ball of cookie dough in half.
Alternate adding each half ball of flavor to your hand, for a total of four pieces of dough (for example - brownie: chocolate chip: brownie: chocolate chip)
Roll the dough into a ball, and repeat with the remaining cookie dough. (Tip: for uniform balls of dough, you can gently press each cookie dough ball into a 3 tbsp. cookie scoop!)
Place the dough balls into an airtight container in the fridge for 30 minutes*
Preheat the oven to 350°F / 175°C.
Evenly space out the cookie dough balls on a parchment lined cookie sheet and top them with extra chocolate.
Bake for 12-14 minutes, or until the edges of the cookies start to turn golden brown.
Once the cookies come out of the oven, I recommend "scooting" them. This just means take a bowl, cup, or biscuit cutter that is slightly larger than the cookie, place it on top of the cookie, and swirl the bowl around to make the cookie a little more round.
Let the cookies sit on the hot baking tray for at least 5 minutes before transferring them to a wire rack to cool. Sprinkle with flaky sea salt, serve and enjoy!