Carefully separate egg yolks from whites; refrigerate egg whites.

In a medium bowl, whisk together yolks and sugar until smooth. Slowly whisk in milk and cream. Set aside.

In another medium bowl, whisk egg whites until two-thirds of mixture is frothy. Stir frothy mixture into yolk mixture. Discard remaining one-third egg whites mixture.

Garnish with nutmeg, if desired. Store sealed in a glass jar in the refrigerator for up to 1 day. Shake jar before mixing cocktails.