On a chilly afternoon in Seoul, the scene outside an ordinary neighborhood subway exit follows a familiar rhythm. Steam billows from large rectangular metal vats under heavy plastic flaps, carrying the savory aroma of simmered kelp, dried anchovies, and sweet-and-spicy chili paste. Commuters in padded winter coats step up to the counter, grab a pair of wooden tongs, and balance a paper cup of hot broth in one hand while spearing food with a long bamboo skewer in the other.