In a medium bowl, whisk together flour, cocoa powders, baking soda, and salt. Set aside.
In the bowl of a stand mixer, beat butter and sugars on med-high until light and fluffy (approx. 2-3mins). Reduce speed and add egg and vanilla. Beat until combined. Add flour mixture and mix until just combined. Add butterscotch chips and mix until just combined.
Chill dough for at least 1 hour or overnight.
Preheat oven to 350F. Using a medium cookie scoop, portion dough onto baking sheet lined with parchment (I did 9 cookies per sheet). Bake for approximately 10 mins, or until the middle is mostly set. Sprinkle with sea salt if desired.
Cool on pans for 5 mins then transfer to to a wire rack to cool completely.
Notes
* If you don't have black cocoa you can substitute Dutch-processed. The cookies won't be as dark though. ** You can substitute any kind of chips you like!