Heat oven to 325. Line baking sheet with parchment paper.

Place chopped chocolate in a small bowl; microwave 1 minute, stir until smooth and set aside to cool slightly.

In a medium bowl, whisk flour, cocoa, baking soda, and salt.

In separate large bowl of stand mixer, beat butter until smooth. Add brown sugar and beat on medium high speed for 5 minutes, occasionally scraping down the sides of the bowl. Add egg and beat 3 minutes longer. Stir in vanilla and melted chocolate. One low speed, beat in flour mixture. Fold in chocolate chunks or chips.

Scoop 2tbsp  of dough, roll into ball, roll in sugar to coat. Place cookies on parchment lined baking sheet and flatten slightly.

Bake cookies at 325°F  for 14 minutes or until cookies begin to crack. Cool on pan for a few minutes then carefully transfer to a wire rack to cool completely.