01 - Place the finely chopped white chocolate in a heatproof bowl.
02 - Pour the eggnog into a small saucepan and heat gently over medium-low until steaming, without allowing it to boil.
03 - Pour the hot eggnog over the white chocolate and allow it to sit for 2 minutes, then whisk slowly until the chocolate is completely melted and smooth.
04 - Stir in the unsalted butter, ground nutmeg, ground cinnamon, vanilla extract, and a pinch of salt until fully combined.
05 - Cover the bowl and refrigerate the ganache for a minimum of 2 hours until the mixture is firm enough to scoop.
06 - Use a teaspoon or melon baller to scoop portions of the chilled ganache, rolling each portion between your palms to form 1-inch balls. Place onto a parchment-lined baking tray and refrigerate for 30 minutes to firm.
07 - Melt the chopped dark chocolate in a heatproof bowl set over a pot of barely simmering water or with short intervals in the microwave, stirring until smooth.
08 - Using a fork, dip each ganache ball into the melted dark chocolate, letting any excess drip away. Return the coated truffles to the parchment-lined tray.
09 - Dust the tops of the truffles lightly with additional ground nutmeg or cinnamon before the chocolate sets, if desired.
10 - Allow the chocolate coating to set fully at room temperature, or refrigerate briefly to speed up the process.