In a heatproof bowl, melt the butter and chocolate chips together using a microwave in 30-second intervals or over a double boiler. Stir until smooth and glossy. Let cool slightly.
In a large mixing bowl, beat together the eggs, granulated sugar, and brown sugar until light and fluffy—about 2–3 minutes. Stir in the vanilla extract and the melted chocolate mixture until fully combined.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Gradually fold this dry mix into the wet mixture until just combined. The dough will be thick and sticky. Chill for 30 minutes to firm up.
Preheat the oven to 350°F (175°C) and line baking sheets with parchment paper. Scoop heaping tablespoons of dough and place 2 inches apart. If desired, press a few extra chocolate chips or chunks on top. Bake for 10–12 minutes, or until the tops are cracked and just set. Let cool on the baking sheet for 5 minutes before transferring to a wire rack.