In a heavy pot, add the eggnog, sugar and butter, then bring to a boil.
Stir the fudge OFTEN - this is important!
Meanwhile line an 8-inch square baking pan with parchment paper and grease lightly.
After about 10 minutes, or when the mixture in the pot reaches 234°F (use a candy thermometer to check) take the pan off the heat.
Stir in the white chocolate until it melts.
Stir in the marshmallow crème.
Stir in the vanilla and half of the nutmeg.
Spread the mixture into the prepared baking pan and sprinkle the rest of the nutmeg on top.
Put the baking pan in the fridge for 4 hours and then cut and serve.