01 - Line an 8x8-inch baking pan with parchment paper, leaving an overhang 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 heat to low and simmer for 4 to 5 minutes, stirring constantly.
04 - Remove saucepan from heat. Add white chocolate chips, ground nutmeg, ground cinnamon, and pure vanilla extract. Stir until chocolate is fully melted and the mixture is smooth.
05 - Pour the fudge mixture into the prepared pan. Smooth the top with a spatula and, if desired, sprinkle with freshly grated nutmeg.
06 - Cool at room temperature for 30 minutes, then refrigerate for at least 2 hours until firm.
07 - Lift the fudge out of the pan using the parchment overhang. Slice into 36 squares with a sharp knife.