Place 8 ounces semisweet chocolate and the unsweetened chocolate in a 4-quart bowl.
Heat the heavy cream in a 1 1/2-quart saucepan over medium heat. Bring to a boil. Pour the boiling cream over the chocolate. Allow to stand for 5 minutes, then stir until smooth (now you have ganache). Refrigerate the ganache for 1 hour until firm but not hard.
Line a baking sheet with parchment paper. Using a tablespoon of ganache for each truffle (approximately 3/4 ounce), portion 24 truffles, evenly space onto the parchment lined baking sheet. Refrigerate the ganache portions for 15 minutes (so the ganache will be firm enough to roll into truffles). When the ganache is firm enough to handle, remove from the refrigerator and individually roll each portion of ganache in your palms, in a gentle circular motion, using just enough pressure to form smooth rounds. Roll 16 of the rounds in 2 tablespoons cocoa and separately roll 8 in the confectioners sugar until completely covered. Store the truffles in a tightly sealed plastic container, in the refrigerator. Remove about 1 hour before serving.