01 - In a large mixing bowl, combine beef broth, cold water, rice vinegar, sugar, soy sauce, sesame oil, and salt. Whisk thoroughly until sugar and salt completely dissolve. Refrigerate the broth mixture until ready to serve—the colder the broth, the better the final dish.
02 - Bring a pot of water to a boil. Cook eggs for 10 minutes for hard-boiled consistency, then immediately transfer to an ice bath before peeling. Thinly slice the cooked beef brisket, cucumber, Asian pear, and optional pickled radish. Set all toppings aside in the refrigerator until assembly.
03 - Bring a large pot of water to a rolling boil. Add naengmyeon noodles and cook according to package directions, typically 3-4 minutes until al dente. Drain thoroughly in a colander, then rinse under cold running water for 1-2 minutes to remove excess starch and chill the noodles completely.
04 - Divide the chilled noodles evenly among four serving bowls. Pour the refrigerated broth over the noodles, ensuring each bowl receives an equal portion. Arrange cucumber slices, pear, beef, and egg halves on top of each serving. Add ice cubes directly to the bowls to maintain the icy temperature.
05 - Sprinkle toasted sesame seeds generously over each bowl. Add a dollop of gochujang on the side for guests who prefer additional heat and spice. Serve immediately while the soup remains thoroughly cold. Offer extra vinegar and mustard at the table for individual seasoning adjustments.