01 - Place chopped white chocolate in a heatproof bowl.
02 - Gently heat eggnog in a small saucepan over medium-low until steaming, without boiling.
03 - Pour hot eggnog over the white chocolate. Allow to sit for 2 minutes, then whisk gently until smooth and melted.
04 - Stir in softened butter, ground nutmeg, ground cinnamon, vanilla extract, and a pinch of salt until fully combined.
05 - Cover bowl and refrigerate for a minimum of 2 hours, or until mixture is firm enough to scoop.
06 - Use a teaspoon or melon baller to portion ganache and roll into 1-inch balls. Arrange on a parchment-lined tray and refrigerate 30 minutes to set.
07 - Melt chopped dark chocolate in a heatproof bowl over a pan of gently simmering water (double boiler) or in the microwave in short bursts, stirring until smooth.
08 - Dip each chilled ganache ball into melted dark chocolate using a fork, allowing excess to drip off before returning to the tray.
09 - Optional: Dust tops lightly with nutmeg or cinnamon before the chocolate sets. Let truffles set at room temperature or chill briefly to firm the coating.