Step 1

Combine the butter and chopped chocolate in a heatproof bowl and set over a saucepan filled with a few inches of simmering water over low heat. Let melt, 3 to 4 minutes, then stir until smooth. Remove the bowl from the pan and let cool slightly.

Step 2

Combine the flour, cocoa powder, baking powder, baking soda and salt in a medium bowl and whisk to combine and get rid of any lumps.

Step 3

Combine the brown sugar, eggs, vanilla and ½ cup granulated sugar in a large bowl and beat with a mixer on medium-high speed until light and smooth, 2 to 3 minutes. Add the melted chocolate mixture and beat until combined. With the mixer on low speed, add the flour mixture and beat until just combined, 30 seconds to 1 minute. Cover the dough and refrigerate until firm, at least 2 hours and up to 4 hours.

Step 4

Preheat the oven to 350˚. Line 2 baking sheets with parchment paper. Spread the remaining 1 cup granulated sugar in a shallow bowl and the powdered sugar in a second shallow bowl. Scoop the dough into balls (about 1 tablespoon each). Roll first in the granulated sugar, then in the powdered sugar to coat completely. Place on the baking sheet, about 2 inches apart. Bake until the tops of the cookies are cracked and the edges are firm, 10 to 12 minutes. Let cool 5 minutes on the baking sheets, then remove to racks to cool completely.