Line an 8-inch square pan with parchment paper and let it hang over the side; set aside.
In a heavy 3-quart saucepan, combine the sugar, butter, eggnog and salt over medium heat. Bring to a rolling boil, stirring constantly. Continue boiling 8 to 10 minutes, until a candy thermometer reaches 234 degrees F, stirring constantly to prevent scorching. Remove from heat.
Using a wooden spoon, work quickly to stir in chopped white chocolate and nutmeg until chocolate is melted and smooth. Stir in marshmallow creme and rum extract. Beat until well blended and then pour into prepared pan. Sprinkle a little freshly ground nutmeg on top. Let stand at room temperature until cooled, then refrigerate overnight until firm.
When completely cool, cut into squares. Store in a covered container in the refrigerator.