01 - Place the finely chopped white chocolate in a heatproof bowl.
02 - Warm the eggnog in a small saucepan over medium-low heat until steaming but not boiling.
03 - Pour the hot eggnog over the white chocolate. Allow to stand for 2 minutes, then gently whisk until fully melted and smooth.
04 - Incorporate the butter, nutmeg, cinnamon, vanilla extract, and a pinch of salt. Mix until evenly combined.
05 - Cover the bowl and chill in the refrigerator for a minimum of 2 hours, until the ganache is firm enough to be shaped.
06 - Using a teaspoon or melon baller, portion out 1-inch round balls. Arrange on a parchment-lined tray and refrigerate for 30 minutes.
07 - Melt the dark chocolate in a heatproof bowl set over barely simmering water or microwave in short bursts, stirring until smooth.
08 - Using a fork, immerse each ganache ball in the melted chocolate. Tap off excess and return to the parchment-lined tray.
09 - Optionally sprinkle with additional nutmeg or cinnamon before the coating sets.
10 - Allow coated truffles to set completely at room temperature or refrigerate briefly to firm before serving.