Put the chocolate in a bowl. In a small saucepan or microwave, heat the cream to a boil. Pour the cream over the chocolate and shake the bowl gently to settle the cream. Cover with a plate or lid and set aside until the chocolate melts, about 5 minutes. Whisk the mixture until smooth and shiny. Stir in the rum or other flavoring. Cover the surface of the chocolate with plastic wrap. Set aside in a cool place until the chocolate firms up, about 2 hours. (To speed this up set the bowl of chocolate over another bowl of ice and stir until the desired consistency.)
Line a baking sheet with waxed or parchment paper. Use 2 spoons to drop small mounds/balls of chocolate, about 1/2 to 1-inch high on the paper (depending on the size you want). Then chill your hands under a faucet of running cold water or by using an ice bath. Roll each chocolate mound between your open palms to make smooth round balls.
Pour the cocoa or coating of choice into a cake pan or on a plate. Roll the truffles in the coating or use a clean spoon to pour the coating on the truffles. Repeat with all the truffles. Refrigerate until ready to serve.
To serve, scoop the truffles out of the cocoa with a fork or a slotted spoon. Put the truffles in small candy cups and serve now or refrigerate until ready to serve.