01 - Line an 8x8-inch baking pan with parchment paper, leaving enough overhang for easy removal.
02 - In a medium saucepan, melt unsalted butter over medium heat. Add eggnog and granulated sugar, stirring frequently until the mixture begins to gently boil.
03 - Reduce heat to low and simmer for 4 to 5 minutes, stirring constantly to prevent scorching.
04 - Remove the saucepan from heat. Add white chocolate chips, ground nutmeg, cinnamon, and vanilla extract. Stir until fully melted and smooth.
05 - Immediately transfer the fudge mixture to the prepared baking pan and smooth the surface with a spatula. Sprinkle evenly with freshly grated nutmeg if desired.
06 - Allow the fudge to cool at room temperature for 30 minutes, then refrigerate for at least 2 hours until firmly set.
07 - Using the parchment overhang, lift the fudge from the pan. Cut into 36 squares with a sharp knife.