In a microwave-safe bowl, melt 1 cup semisweet chocolate chips, the unsweetened chocolate and the butter. Stir until smooth, then let it cool for 10 minutes.
In a large mixing bowl, beat the sugar and eggs for two minutes until light and fluffy. Then beat in the chocolate mixture and vanilla extract until well combined.
In another bowl, whisk together the flour, cocoa, baking powder and salt. Gradually beat the dry ingredients into the chocolate mixture. Stir in the remaining semisweet chocolate chips.
Refrigerate the dough, covered, until it's firm enough to handle, at least three hours.
Preheat the oven to 350°F. With lightly floured hands, shape the dough into 1-inch balls and place them 2 inches apart on ungreased baking sheets.
Bake the cookies until they're lightly puffed and set, 10 to 12 minutes. Let them cool on the pans for three minutes, then transfer them to wire racks to cool completely. Dust with confectioners' sugar before serving.
