Inside each jar of yuja-cha—a type of concentrated Korean citron tea that looks like marmalade—is a winter's worth of invigorating, soothing, sweet-tart warmth. Made by curing sour citron (also known as yuzu) in an intense syrup of honey and sugar, a heaping tablespoon of the stuff melts gracefully into a mug of hot water with a puff of bracing citric steam. Korean markets have whole aisles dedicated to yuja-cha—it's a popular home remedy for the common cold—but we look past the jars flavored with ginger or other warm spices and home in on those with the fewest ingredients on the label. In our opinion, all you need is citron and sweetness for the perfect sip.