01 - Place chopped white chocolate into a heatproof bowl.
02 - Warm eggnog in a small saucepan over medium-low heat until steaming, without allowing it to boil.
03 - Pour the hot eggnog over the white chocolate and let it stand for 2 minutes.
04 - Gently whisk the mixture until the chocolate is completely melted and smooth.
05 - Stir in softened butter, ground nutmeg, ground cinnamon, vanilla extract, and a pinch of salt until fully combined.
06 - Cover the bowl and refrigerate for at least 2 hours, or until the ganache is firm enough to scoop.
07 - Using a teaspoon or melon baller, scoop the chilled ganache and roll into 1-inch balls. Arrange on a parchment-lined baking tray.
08 - Refrigerate the shaped ganache balls for 30 minutes to allow them to firm.
09 - Melt dark chocolate in a heatproof bowl over a pan of barely simmering water or using short intervals in a microwave, stirring until smooth.
10 - Using a fork, dip each chilled ganache ball into the melted dark chocolate, allowing excess to drip off, and return to the parchment-lined tray.
11 - Optionally, dust the tops with a pinch of ground nutmeg or cinnamon before the chocolate coating sets.
12 - Allow truffles to set at room temperature or briefly refrigerate until the chocolate coating is firm.