Step 1

Beat the egg yolks until thick and pale yellow in a medium-size bowl with a mixer set to high speed. Gradually add ⅓ cup sugar and continue beating until the sugar dissolves.

Step 2

Stir together the milk, 1 cup cream, and ½ teaspoon nutmeg in a small saucepan. Bring just to a simmer over medium heat. Whisking constantly, add the warm milk mixture to egg yolk mixture in a slow, steady stream. Pour into the saucepan and cook over medium heat, stirring constantly with a heat-proof spatula until the mixture thickens slightly and reaches 160°F. Pour into a bowl. Stir in the liquor, if using. Cover and refrigerate until chilled.

Step 3

Just before serving, beat the egg whites to soft peaks in a medium-size bowl with a mixer set to high speed. Add the remaining 1 tablespoon sugar and beat to firm peaks. Fold into the chilled base mixture.

Step 4

Beat the remaining 1 cup cream to stiff peaks, and then fold into eggnog. (Alternatively, fold half the whipped cream into the chilled base and spoon the rest on top as garnish.)

Step 5

Serve chilled, garnished with nutmeg.