01 - Line an 8x8-inch baking pan with parchment paper, allowing overhang for easy removal.
02 - In a medium saucepan set over medium heat, combine unsalted butter, eggnog, and granulated sugar. Stir 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, ground cinnamon, and vanilla extract. Stir until all chocolate is fully melted and mixture is smooth.
05 - Promptly pour the fudge mixture into the prepared baking pan. Smooth the surface using a heatproof spatula.
06 - Evenly sprinkle freshly grated nutmeg over the surface, if using. Allow to cool at room temperature for 30 minutes, then refrigerate for a minimum of 2 hours or until completely set.
07 - Remove fudge block from the pan with the parchment overhang. Using a sharp knife, cut into 36 even squares.