In a small saucepan, melt bittersweet chips over low heat. Transfer to a bowl; cool to lukewarm, about 7 minutes.
Beat in whipped topping and cinnamon. Place in the freezer for 15 minutes or until firm enough to form into balls. Shape mixture into 1-in. balls.
In a microwave, melt milk chocolate chips and shortening; stir until smooth. Dip truffles in chocolate and place on waxed paper-lined baking sheets. Immediately sprinkle with toppings of your choice. Refrigerate until firm. Store in an airtight container in the refrigerator.