1. Add the heavy cream and eggnog to a small saucepan and warm over low heat until hot but not boiling.

2. Place the chopped white chocolate in a heatproof bowl, then pour the warm cream mixture over it.

3. Add the ground nutmeg and vanilla extract, let it sit for 1 minute, then stir until smooth and glossy.

4. Cover the bowl and refrigerate the mixture for 2 to 3 hours, or until firm enough to scoop.

5. Scoop small portions of the chilled filling and roll into 1-inch balls. Place them on a parchment-lined tray.

6. Chill the rolled centers in the freezer for 15 to 20 minutes so they stay firm for dipping.

7. Melt the dark chocolate gently in the microwave or over a double boiler until smooth.

8. Dip each truffle center into the melted dark chocolate, let the excess drip off, and return to the tray.

9. Drizzle the tops with melted white chocolate and sprinkle with crushed cookie crumbs and a tiny pinch of nutmeg if desired.

10. Refrigerate until the coating is fully set, then serve chilled or slightly softened at room temperature.