1. Combine chocolate and cream in a microwave-safe container. Heat in a microwave oven at 50 percent power, stirring twice, until chocolate is soft, 1 1/2 to 2 minutes total. Remove from oven and stir until mixture is smooth.
2. Using plastic wrap, smoothly line the bottom and at least 1 inch up the sides of a 4- by 8-inch loaf pan.
3. Pour chocolate mixture into pan. Chill up to 1 hour or freeze up to 30 minutes until firm when pressed.
4. Sprinkle cocoa over a sheet of waxed paper on a cutting board. Lift chocolate slab out of pan and turn over onto cocoa; peel off plastic wrap.
5. With a knife, immediately cut slab into 3/4-inch squares (some chocolates are too brittle to cut neatly; irregular pieces are fine).
6. Lift edges of waxed paper and tilt back and forth to completely coat chocolate pieces with cocoa. Lift truffles, shake off excess cocoa, and put truffles on a serving dish.
7. Serve cold or at room temperature.
Nutritional analysis per piece.