FREEZE THE CHOCOLATE CENTERS: Place 12 squares of dark chocolate on a plate or tray and freeze for at least 30 minutes to help them stay intact during baking.
MELT BUTTER AND CHOCOLATE: In a heatproof bowl, melt the butter and chocolate chips over a double boiler or in the microwave in short intervals, stirring between bursts until smooth. Set aside to cool slightly.
WHISK WET INGREDIENTS: In a large bowl, whisk the granulated sugar, brown sugar, eggs, and vanilla extract together until the mixture is pale and thick, about 2 to 3 minutes.
COMBINE WITH MELTED CHOCOLATE: Stir the cooled chocolate mixture into the sugar and egg mixture until fully blended and smooth.
ADD DRY INGREDIENTS: In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Fold the dry ingredients into the wet mixture just until combined. The dough will be soft and sticky.
CHILL THE DOUGH: Cover the dough and refrigerate for at least 1.5 to 2 hours, or overnight, to firm it up and prevent spreading during baking.
SHAPE, COAT, AND BAKE: Preheat the oven to 350°F (175°C) and line a baking tray with parchment paper. Scoop out 2 tablespoons of dough, flatten it in your palm, place a frozen chocolate square in the center, and wrap the dough around to form a ball. Roll each dough ball in granulated sugar, then coat thoroughly in powdered sugar. Place on the prepared tray, spacing cookies 2 inches apart. Bake for 11 to 13 minutes, until the tops are cracked and the edges are set. Let cool on the tray for 5 minutes before transferring to a wire rack.