01 - Place the finely chopped white chocolate into a heatproof bowl.
02 - Warm eggnog in a small saucepan over medium-low heat until steaming but not boiling.
03 - Pour hot eggnog over the white chocolate. Allow to stand for 2 minutes, then gently whisk until smooth.
04 - Fold in softened butter, ground nutmeg, ground cinnamon, vanilla extract, and a pinch of salt into the melted mixture. Mix thoroughly.
05 - Cover the bowl and refrigerate for a minimum of 2 hours until the ganache is firm enough to scoop.
06 - Using a teaspoon or melon baller, portion chilled ganache and roll into 1-inch balls. Arrange on a parchment-lined tray. Refrigerate for 30 minutes to set.
07 - Melt chopped dark chocolate in a heatproof bowl over simmering water or microwave in short intervals, stirring until completely smooth.
08 - Using a fork, dip each chilled ball into the melted dark chocolate, allowing excess to drip off. Return coated truffles to the parchment-lined tray.
09 - Before the coating sets, dust with additional nutmeg or cinnamon, if desired.
10 - Let truffles set at room temperature, or refrigerate briefly until the coating is fully firm.