Heat semisweet and unsweetened chocolate, sweetened condensed milk and salt in saucepan over medium heat, stirring, until chocolate is melted, 7 minutes. Remove from heat. Add liqueur if using, and nuts and cherries.
Cover surface directly with waxed paper; refrigerate until cold, 1-1/2 hours.
Using measuring tablespoon, or spoon, scoop out slightly heaping tablespoon chocolate mixture; roll into smooth ball between hands. Place on waxed paper-lined baking sheet. Continue with remainder.
Melt white chocolate with oil in small saucepan over low heat, stirring. Let stand until cool to touch, 1 minute. Using 2 forks, dip balls into white chocolate. Transfer to waxed paper to dry. Decorate with sprinkles.
Makes 42 truffles.