01 - Line an 8x8-inch baking pan with parchment paper, allowing excess to hang over the edges for easy removal.
02 - Combine unsalted butter, eggnog, and granulated sugar in a medium saucepan over medium heat. Stir frequently until gently boiling.
03 - Lower the heat and simmer for 4 to 5 minutes, maintaining constant stirring to prevent scorching.
04 - Remove saucepan from heat. Add white chocolate chips, ground nutmeg, ground cinnamon, and vanilla extract. Stir until fully melted and smooth.
05 - Immediately transfer the mixture to the prepared pan and smooth the surface using a spatula.
06 - Evenly sprinkle freshly grated nutmeg over the surface if desired.
07 - Let set at room temperature for 30 minutes, then refrigerate at least 2 hours until completely firm.
08 - Use the parchment to lift the set fudge from the pan. Cut into 36 evenly sized squares with a sharp knife.