01 - Line an 8x8-inch baking pan with parchment paper, ensuring enough overhang to lift the fudge out after chilling.
02 - In a medium saucepan over medium heat, combine unsalted butter, eggnog, and granulated sugar. Stir regularly until the mixture reaches a gentle boil.
03 - Reduce the 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, ground cinnamon, and pure vanilla extract. Stir until the chocolate chips are fully melted and the mixture is smooth and uniform.
05 - Immediately transfer the fudge mixture into the prepared baking pan. Use a spatula to smooth the surface evenly.
06 - If desired, sprinkle the top evenly with freshly grated nutmeg.
07 - Allow the fudge to cool at room temperature for 30 minutes, then refrigerate for at least 2 hours or until completely firm.
08 - Lift the set fudge from the pan using the parchment paper overhang and cut into 36 small squares using a sharp knife.