Used in batter recipe for fried chicken
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Creative use of eggnog!! Buttermilk is traditional. You will get tang without the sweetness or spice of eggnog. I suspect kefir (unflavored), that is, drinkable yogurt would work, too. Same with regular yogurts since you are using the dairy product as a marinade; think tandoori chicken. In a pinch, sour milk by adding a little bit of vinegar or lemon juice, stir, then wait 5-10 minutes till it thickens.
Buttermlk IS trad, but you are asking about eggnog, yes? I'm guessing you want to make eggnog, since you can't find any in stores this time of year? If so, the you'll just look up recipes for eggnog, which usually contains milk or cream,egg, sugar,some hard alcohol like brandy, rum or bourbon; nutmeg, allspice, cinnamon....