In a medium saucepan on low heat melt semi-sweet chocolate with the condensed milk and stir until well blended.
Remove from heat; stir in vanilla and coffee flavoring.
Pour the chocolate mixture into a 2-quart baking dish and refrigerate for about 1 hour.
Remove dish from the refrigerator and stir to make sure the chocolate is slightly cooled and no longer warm (chocolate should be soft enough to be able to roll in the coating).
Using a melon baller or 1-inch cookie scoop, scoop the chocolate and lightly shape into 1-inch balls by rolling between the palms of your hands (I like to weigh the chocolate to .3 ounces each so the candies are uniform).
Roll each truffle in the desired coating until well covered.
Place the coated truffles on a sheet pan lined with parchment paper.
Chill 1 hour or until firm.
Store tightly in a covered container. Truffles will last for up to six months if refrigerated.