01 - Line an 8x8-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
02 - In a medium saucepan over medium heat, combine unsalted butter, eggnog, and granulated sugar. Stir frequently until the mixture reaches a gentle boil.
03 - Reduce the heat to low and simmer for 4 to 5 minutes, stirring constantly to prevent burning.
04 - Remove the saucepan from heat. Add white chocolate chips, ground nutmeg, ground cinnamon, and pure vanilla extract. Stir until the chocolate chips are fully melted and the mixture is smooth.
05 - Immediately pour the hot fudge mixture into the prepared baking pan and smooth the surface with a spatula.
06 - Evenly sprinkle freshly grated nutmeg over the top, if desired.
07 - Let the fudge cool at room temperature for 30 minutes, then transfer to the refrigerator and chill for at least 2 hours or until completely firm.
08 - Using the parchment overhang, lift the fudge from the pan and cut into 36 squares with a sharp knife.