Using a melon baller or small ice cream scoop, spoon out balls from the tray of tiramisu to create the bon bons. Freeze the bon bons on a cookie sheet for at least 1 hour or overnight.
Melt the bittersweet chocolate in a double boiler until smooth and glossy. Dip frozen tiramisu bon bons in melted chocolate until covered on all sides. Place the bon bons on a cookie sheet covered in parchment or waxed paper and return them to the freezer. Take bon bons out of freezer and let them thaw for about 15 minutes before serving.