01 - Place the finely chopped white chocolate in a heatproof bowl.
02 - Gently warm eggnog in a small saucepan over medium-low heat until steaming, without boiling.
03 - Pour hot eggnog over the white chocolate. Allow to sit for 2 minutes, then whisk gently until the mixture is smooth and fully melted.
04 - Stir in the softened butter, ground nutmeg, ground cinnamon, vanilla extract, and a pinch of salt until combined.
05 - Cover the bowl and refrigerate for at least 2 hours, or until the ganache is firm enough to scoop.
06 - Scoop chilled ganache using a teaspoon or melon baller. Roll into 1-inch balls and arrange on a parchment-lined baking tray. Refrigerate for 30 minutes until set.
07 - Melt the chopped dark chocolate in a heatproof bowl set over barely simmering water (double boiler) or in short intervals in the microwave. Stir until completely smooth.
08 - Using a fork, dip each ganache ball in the melted dark chocolate, letting the excess drip away. Return to the parchment-lined tray.
09 - Optionally dust each truffle with a pinch of nutmeg or cinnamon before the chocolate sets.
10 - Allow the truffles to set completely at room temperature or briefly chill to firm the chocolate shell.