Place 2/3 cup eggnog in a medium bowl, sprinkle gelatin over top, stir to combine.
Let gelatin “bloom” and become completely hydrated. Approximately 5 minutes.
Place mixture in microwave and heat for 1 minute on high. Stir. Continue microwaving in 15 second intervals until the gelatin is melted, stirring between each.
Put corn syrup, butter, glycerin, vanilla, and salt in a medium glass bowl, add this mixture to the melted gelatin. Stir.
Microwave mixture for 2 minutes on high setting. Butter should be melted. Stir, set aside to cool to luke warm to the touch, or place in the freezer and stir every few minutes to equalize the temperature until it is luke warm.
Sift half of the powdered sugar into the mixer bowl.
Strain the luke warm liquid mixture into the powdered sugar and sprinkle a cup of powdered sugar over top.
Place the bowl on the mixer fitted with the dough hook attachment and mix at low speed.
Continue to add powdered sugar, about a cup at a time including the nutmeg, until fondant forms a soft ball. It should not slide down the dough hook and there may be some powdered sugar left in the bottom of the bowl.
When fondant is ready (and it will still be sticky), remove from the bowl and knead in small amounts of powdered sugar until the fondant is smooth. It should still be slightly soft.
Coat in shortening and plastic wrap; wrap again, and then place in a Ziploc bag.
Allow fondant to rest over night. The flavor will develop beautifully.