Add egg yolks and sugar to a large mixing bowl and whisk until light yellow.
Add the milk and whipping cream and whisk until blended.
Add pumpkin puree and whisk until well incorporated.
Pour into a saucepan and heat over medium heat until it reaches 160 degrees. Ensure to stir constantly to avoid scorching.
Remove from heat and allow to cool for about 5 minutes.
Stir in vanilla, cinnamon and nutmeg until well blended.
Cool in the refrigerator and enjoy within 24 hours.
Tip: You can whisk the egg whites into a meringue and incorporate into your eggnog right before the cook step to get a lighter result.