In a large saucepan, stir together sugar and flour. Gradually stir in the milk. Bring to a boil over medium heat. In a small bowl, whisk egg yolks until smooth. Ladle a small amount of the hot milk into the yolks and quickly whisk in. Pour the tempered yolk mixture back into the hot milk. Cook, stirring constantly, until mixture comes to a boil. Remove from heat and allow to cool.
In a medium glass or metal bowl, beat egg whites until foamy. Gradually add 4 teaspoons sugar, continuing to beat until stiff peaks form. fold whites into eggnog and refrigerate until chilled. Serve garnished with a dollop of whipped cream and a dash of nutmeg.