Bring the milk, half and half, cinnamon sticks, vanilla bean and nutmeg just to a boil in a medium saucepan on low heat.
Beat egg yolks and sugar in medium bowl until pale yellow in color and fluffy.
Gradually add one cup of the hot milk mixture to the egg yolks, beating with a wire whisk on low speed..
Gradually whisk the egg yolk, sugar and milk mixture back into the remaining milk in the saucepan.
Cook and stir on medium-low heat for 3 – 5 minutes or until mixture thickens and coats the back of a spoon. Do not rush this stage or your mixture could curdle.
Strain into a large bowl. Pour into a container and allow to cool. Add bourbon, cover tightly and refrigerate overnight or until well chilled. Best if allowed to meld for 2-3 days but can be served immediately.
Fill lowball glasses with ice, pour bourbon eggnog mixture over ice and dust with nutmeg.
If wanting to serve without the bourbon; simply follow the directions as given and omit the liquor.