In a heatproof bowl, melt chopped chocolate with butter until smooth. Cool slightly.
In a separate bowl, whisk eggs, granulated sugar, brown sugar, and vanilla until pale and thick (about 2–3 minutes).
Stir the cooled chocolate mixture into the egg mixture.
In another bowl, whisk flour, cocoa, baking powder, and salt. Fold gently into the wet mixture. Add extra chocolate chips if using.
Refrigerate dough for 30 minutes for easier scooping.
Preheat oven to 350°F (175°C). Line baking sheets with parchment. Scoop 2-tbsp mounds of dough spaced apart.
Bake 10–12 minutes, until tops are crackly but centers still soft.
Let rest on pan 5 minutes, then move to wire rack. Enjoy warm or cooled.
