Melt the butter, then whisk in both sugars.
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 no flour streaks remain.
Divide the dough evenly between three bowls (approximately 150g per bowl)
To each bowl, gently fold in one of the cocoa powders until almost fully combined. Then, add in 1/3 of the chocolate (50g / 4.5 tbsp.) to each bowl and mix until just combined.
Use a 1 tbsp. cookie scoop to dish out heaping tablespoons of each flavor of dough. Then, use a knife or your hands to split each cookie dough ball in half.
Alternate adding each half ball of flavor to your hand, six pieces total. Roll the dough into a ball. Repeat until you have used all of the pieces.
Tip: If you want the balls of cookie dough to be a little more uniform, you can gently press them into a 3 tbsp. cookie scoop!
Chill the dough in the fridge for at least 20 min. to allow it to firm up and avoid over-spreading in the oven. If you want thinner cookies, you can bake them right away.
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 10-12 minutes, or until they have set.
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!