1. Preheat oven to 375 degrees Fahrenheit. Line two baking sheets with parchment paper.
2. Into a stand mixer fitted with the paddle attachment, mix together butter and sugars on medium speed until pale, about 5 minutes.
3. Meanwhile, whisk together flour, salt, baking powder, and baking soda in a separate bowl. Set aside.
4. Roughly chop chocolate bar. Set aside.
5. To the butter mixture, mix in egg and extract until evenly incorporated.
6. Turn the mixer off. Add in flour mixture in 2-3 turns, pulsing mixer to combine. When there’s just a slight trace of flour left, add in chocolate. Continue to pulse until just combined. Over-mixing flour will yield a tough cookie.
7. Using a 2 oz. spring-release ice cream scoop, scoop 6 cookies per baking sheet. They’ll look like scoops of ice cream. Don’t flatten. Bake for 10 minutes. Cookies will seem undercooked straight out of the oven. Allow to continue cooking on the pan for 2 minutes before carefully removing to a cooling rack to cooling completely, at least an hour. I like them best the next day. Store covered in an airtight container for up to 3 days.
Notes: If making smaller cookies, reduce baking time by about 2 minutes.