Separate egg whites from yolks. Place egg yolks in a medium mixing bowl and set the egg whites aside (you can use them for another recipe as they will keep in the refrigerator for two days and in the freezer for up to three months.)
Add sugar to the egg yolks and whisk vigorously until the mixture is pale yellow and fluffy. Set aside.
In a medium saucepan, heat milk, whipping cream, and ½ teaspoon freshly ground nutmeg over medium heat until just before it boils. Bubbles will form around the top edge of the milk mixture, and it will begin to steam.
Remove from heat.
To temper the eggs, spoon one ladle full of the hot milk mixture and whisk it into the egg mixture. Continue adding ladles of the hot milk to the egg mixture until most have been added.
Slowly drizzle the egg mixture back into the saucepan, whisking as you do so.
Heat over medium, stirring constantly, until the mixture begins to thicken. DO NOT BOIL. The mixture should not be heated above 160°F.
Remove from heat and stir in vanilla extract and bourbon.
Cover with plastic wrap and place in the refrigerator to cool for at least 1 hour.
Serve with freshly grated nutmeg.