1. In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt until well combined and no cocoa lumps remain.

2. In a heatproof bowl, combine the butter and chopped semisweet chocolate. Melt in short bursts in the microwave or over a pan of gently simmering water, stirring until smooth and glossy. Set aside to cool slightly.

3. In a large mixing bowl, whisk together the 3/4 cup granulated sugar, brown sugar, and eggs until the mixture is thick, smooth, and slightly lightened in color. Whisk in the vanilla extract.

4. Slowly pour the lukewarm melted chocolate mixture into the sugar-and-egg mixture, whisking constantly until fully combined.

5. Switch to a spatula and gently fold the dry ingredients into the chocolate mixture just until no streaks of flour remain. The dough will be thick and sticky, similar to brownie batter.

6. Cover the bowl and refrigerate the dough for 45–60 minutes, or until it is firm enough to scoop and roll without sticking badly to your hands.

7. Near the end of the chill time, preheat the oven to 350°F (180°C). Line two baking sheets with parchment paper or silicone baking mats.

8. Place the remaining 1/3 cup granulated sugar in one shallow bowl and the powdered sugar in another. Scoop the chilled dough into equal portions (about 1 1/2 tablespoons each) and roll each portion into a smooth ball.

9. Roll each dough ball first in the granulated sugar to coat, then in the powdered sugar, making sure it is generously covered. Arrange the coated dough balls on the prepared baking sheets, spacing them about 2 inches apart.

10. Bake the cookies for 9–11 minutes, or until they are puffed, the tops are cracked, and the edges are just set while the centers still look slightly soft.

11. Allow the cookies to cool on the baking sheets for 5 minutes, then transfer them to a wire rack to cool completely. The centers will continue to set as they cool, staying soft and fudgy.

12. Once cool, store the cookies in an airtight container at room temperature for up to 4–5 days, or freeze for longer storage.