Combine sugar, butter and eggnog into a heavy sauce pan and bring to a boil over medium heat. Once boiling, attach a candy thermometer and reduce the heat to a hair above medium low and cook for 10-15 minutes until your thermometer reads 234°F , stirring constantly.
Once your mixture hits the appropriate temperature, remove from heat and add chocolate stirring vigorously until chocolate is melted and smooth. Add the marshmallow creme, nutmeg and rum extract and mix until well blended.
Pour the mixture into your pan and sprinkle with crushed peppermints. Allow to cool on a wire rack until room temperature.
Recipe by Kitchen Meets Girl at https://kitchenmeetsgirl.com/eggnog-fudge/