Whisk egg yolks and sugar in a medium bowl until light and creamy.
Heat milk, cream, nutmeg, and salt in a saucepan over medium-high heat, stirring often until mixture reaches a bare simmer.
Temper the eggs by slowly adding some hot milk to the egg mixture. Repeat, adding a big spoonful at a time while whisking vigorously.
Return everything to the saucepan and whisk constantly for a minute or so, until the mixture is just slightly thickened (or reaches 160 degrees F on a digital thermometer). It will thicken more as it cools.
Add vanilla and alcohol, if using.
Strain the mixture into a pitcher or other container and chill the mixture.
Serve cold with a sprinkle of nutmeg and fresh whipped cream.
