01 - Place the 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 the hot eggnog over the white chocolate and let stand for 2 minutes. Whisk gently until completely melted and smooth.
04 - Stir in softened butter, ground nutmeg, ground cinnamon, vanilla extract, and a pinch of salt until fully incorporated.
05 - Cover the bowl and refrigerate for at least 2 hours, until the ganache has set and is scoopable.
06 - Scoop firm ganache using a teaspoon or melon baller and roll into 1-inch balls. Arrange on a parchment-lined tray and refrigerate for 30 minutes to firm.
07 - Melt the dark chocolate in a heatproof bowl set over a barely simmering pan of water or in the microwave, stirring until glossy and smooth.
08 - Using a fork, dip each chilled ganache ball into the melted dark chocolate, allowing excess to drip off. Place coated truffles back on the parchment-lined tray.
09 - Lightly dust truffle tops with a pinch of nutmeg or cinnamon before chocolate sets.
10 - Allow truffles to set fully at room temperature, or chill briefly to ensure the coating is firm.