In a large bowl, whisk together 1½ cups prepared eggnog base with ¼ cup of powdered erythritol and nutmeg.
In a small bowl, whisk together 2 tbsp of water and the gelatin powder. Microwave on high for 30 seconds and whisk to disolve. Then slowly whisk into eggnog mixture.
In a large bowl, whip 2 cups of heavy cream till soft peaks form. Add ¼ cup powdered erythritol and vanilla extract, and beat an additional 20 seconds till combined.
Fold in ¾ of the whipped cream into you eggnog base ensure it is fully combined (without any large clups or streaks).
Pour pie filing into prepared pie crust and chill in the refrigerator for at least 3 hours (overnight is even better).
With remaining whipping cream, add 2 tbsp of the eggnog base and stir to combine. Top the pie with the whipped cream and garnish with additional nutmeg.