Prepare a square 8x8 pan by lining it with aluminum foil or parchment paper and buttering.
Combine butter, eggnog and sugar in a large saucepan. Heat over medium-high heat stirring frequently. Keep heating and stirring until the mixture reaches a full boil.
Simmer on medium heat until a candy thermometer reads 235.
Remove the pan from the heat.
Add in white chocolate chips, marshmallow cream, and ½ tsp nutmeg. Stir until the chocolate chips have melted completely and all of the ingredients are well incorporated.
Pour the mixture into the prepared pan.
Sprinkle the top of the fudge evenly with ½ tsp of nutmeg.
Place in the refrigerator for at least 4 hours or until completely set.
Cut into 16 pieces and serve.
Store refrigerated in an airtight container.