In a microwave, melt 1 cup chocolate chips, unsweetened chocolate and butter; stir until smooth. Cool 10 minutes., In a large bowl, beat sugar and eggs 2 minutes. Beat in chocolate mixture and vanilla. In another bowl, whisk flour, cocoa, baking powder and salt; gradually beat into chocolate mixture. Stir in remaining chocolate chips. Refrigerate, covered, until firm enough to handle, at least 3 hours., Preheat oven to 350°. With lightly floured hands, shape dough into 1-in. balls; place 2 in. apart on ungreased baking sheets. Bake until lightly puffed and set, 10-12 minutes. Cool on pans 3 minutes. Remove to wire racks to cool. Dust with confectioners' sugar.