If you're not a fan of eggnog flavor, you can use 3 tablespoons heavy cream instead of the egg white. Or you can combine the two: Whip them separately and then fold egg white into the cream.
To make it more of an Irish coffee, simply use Irish whisky! Bushmills(R) Original will work just fine here! I used a simple Scotch single malt for this one, hence it's "Celtic" not purely Irish coffee.
This recipe contains raw egg. We recommend that pregnant women, young children, the elderly, and the infirm do not consume raw egg. Learn more about egg safety from our article, Making Your Eggs Safe.