What is "kongguksu"

Kongguksu is a seasonal Korean noodle dish served in a cold soy milk broth. It comprises noodles made with wheat flour and soup made from ground soybeans. It is unknown when Korean people started eating kongguksu; however, in accordance with the mention of the dish along with kkaeguksu (깨국수, sesame noodle soup) in Siui jeonseo, a Joseon cookbook published around the late 19th century, it is presumed to have originated at least as early as the 19th century.