Use a stand mixer or hand mixer to beat butter on medium speed until soft and fluffy, about 3 minutes.
Add cocoa powder and mix for one minute or until well combined.Add sugar and continue beating until well incorporated, about 1 minute. Add flaky sea salt and beat briefly to combine. Add flour and mix on low until flour is incorporated. Dough will be crumbly.
Add chopped chocolate, stir until combined. Dough will be crumbly still.