01 - Line an 8x8-inch baking pan with parchment paper, ensuring overhang for easy removal.
02 - In a medium saucepan over medium heat, combine the 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 to prevent scorching.
04 - Remove saucepan from heat. Incorporate white chocolate chips, ground nutmeg, ground cinnamon, and pure vanilla extract. Stir until the chocolate is fully melted and the mixture is smooth and cohesive.
05 - Immediately pour the mixture into the prepared baking pan. Smooth the surface with a spatula and, if desired, sprinkle freshly grated nutmeg evenly on top.
06 - Cool at room temperature for 30 minutes. Transfer to the refrigerator and chill for at least 2 hours or until firm throughout.
07 - Use the parchment overhang to lift the set fudge from the pan. Cut into 36 even squares with a sharp knife.