Melt bittersweet chocolate in the top of a double boiler over hot water or in a microwave oven. Let cool. Melt butter; cool. Pour cooled butter into bowl of electric mixer and slowly add evaporated milk. Add cooled chocolate and rum. Cover and refrigerate until mixture sets up, about 1 hour. Form into small balls, using the small end of a melon baller or rolling with your hands. Freeze balls until firm. Once frozen, balls may be put into an airtight container and kept frozen until you are ready to dip them.
Melt white chocolate in a small bowl over hot water or in a microwave oven. Crush candy and spread on a piece of waxed paper. Taking about 10 truffles from the freezer at a time, dip balls in white chocolate, lift out with a fork, let excess run off, then drop onto crushed peppermint candy and roll to cover. Let harden. Store in an airtight container in single layers; keep in a cool place.