Line an 8x8 inch pan with parchment paper, leaving an overhang on the sides, and set aside.

Combine sugar, butter, and evaporated milk in a large saucepan; bring to a rolling boil over medium heat, stirring constantly, and boil for exactly 5 minutes.

Remove the saucepan from heat and immediately stir in the marshmallow cream, white chocolate chips, eggnog, vanilla extract, nutmeg, and salt until smooth and fully combined.

Pour the hot fudge mixture into the prepared pan, spreading it evenly with a spatula, and allow it to cool completely at room temperature before chilling in the refrigerator for at least 2 hours to set firmly.

Once set, use the parchment paper overhang to lift the fudge from the pan, cut it into small squares, and store in an airtight container at room temperature.