01 - Whisk together the all-purpose flour, unsweetened cocoa powder, baking powder, and salt in a medium mixing bowl. Set aside.
02 - Place 6 ounces of chopped semi-sweet chocolate and the unsalted butter in a microwave-safe bowl. Microwave in 30-second bursts, stirring after each, until thoroughly melted and smooth. Allow to cool slightly.
03 - In a large mixing bowl, blend granulated sugar, packed brown sugar, eggs, and vanilla extract until well incorporated.
04 - Pour the melted chocolate and butter into the sugar and egg mixture. Stir until fully smooth.
05 - Gradually fold the dry ingredients into the wet mixture until just combined; do not overmix. The dough should be thick and sticky.
06 - Cover the dough and refrigerate for at least 30 minutes to firm up before shaping.
07 - Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
08 - Divide chilled dough into 12 equal portions. Flatten each, place a chocolate chunk in the center, and fold dough around the chocolate, sealing completely.
09 - Arrange the cookie dough balls on prepared baking sheets, spacing approximately 2 inches apart. Bake for 10–12 minutes, until edges are set and tops appear crackly but centers remain soft.
10 - Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack. Serve warm to enjoy the molten center.