01 - Line an 8x8-inch baking pan with parchment paper, leaving an overhang to easily lift out the fudge.
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 - Lower heat to a simmer and continue stirring constantly for 4 to 5 minutes.
04 - Remove the saucepan from heat. Add white chocolate chips, ground nutmeg, ground cinnamon, and vanilla extract. Stir until fully melted and smooth.
05 - Transfer the fudge mixture into the prepared pan and smooth the surface with a spatula.
06 - Sprinkle the top evenly with freshly grated nutmeg if desired.
07 - Let the fudge cool at room temperature for 30 minutes, then refrigerate for at least 2 hours or until set.
08 - Lift the fudge out of the pan using the parchment overhang and cut into 36 even squares with a sharp knife.