In a heavy 4-quart saucepan with wire whisk, beat eggs, sugar, and salt until
blended. Gradually stir in 1 quart milk and cook over low heat, stirring constantly
or until custard thickens and coats the back of a spoon well — about 25 minutes.
Mixture should be about 160 degrees F, but do not boil or it will curdle.
Pour custard into a large bowl; stir in rum, vanilla extract, ground nutmeg,
and remaining milk. Cover and refrigerate until well chilled, at least 3 hours.
To serve, in small bowl, with mixer at medium speed, beat heavy or whipping cream
until soft peaks form. With wire whisk, gently fold whipped cream into custard mixture.
Pour eggnog into chilled 5-quart punch bowl; sprinkle with nutmeg for garnish.