Line an 8x8-inch baking dish with parchment paper or foil, leaving an overhang for easy removal. Lightly grease with non-stick spray or butter.

In a medium saucepan, combine granulated sugar, butter, and eggnog. Place over medium heat and stir constantly until the butter melts and the mixture begins to boil.

Attach a candy thermometer to the saucepan. Continue stirring as the mixture boils and reaches 234°F (soft ball stage). This will take about 4-5 minutes.

Remove the saucepan from heat and quickly stir in vanilla extract, rum extract (if using), nutmeg, cinnamon, and marshmallow creme. Stir until smooth and fully combined.

Add the white chocolate chips to the mixture and stir until completely melted and smooth.

Pour the fudge into the prepared baking dish. Use a spatula to spread it evenly and gently tap the pan on the counter to release any air bubbles.

Let the fudge cool at room temperature for 1 hour, then transfer it to the refrigerator for 2-3 hours to set completely.

Once the fudge is firm, use the parchment or foil overhang to lift it out of the pan. Cut into small squares and dust with extra nutmeg if desired.