Add dark soy sauce, mirin, Cheongju, and sugar to a pot and bring to a boil.

Cold Buckwheat Noodles (Naeng-momil)
Jang Ho-jun's cold buckwheat noodle recipe, featuring a refreshing, rich broth and chewy noodles.
What You'll Need
Instructions
Cut the green onion and seaweed appropriately for garnish.
Rinse the chopped green onion in water several times to remove the sharp taste and enhance the aroma.
Peel the radish and grate it using a grater.
Rinse the grated radish in water, strain it through a sieve, and squeeze out the moisture to remove the spicy and bitter taste.
Add katsuobushi to the soy sauce broth after the alcohol has evaporated from boiling, and let it steep.
Pour the broth through a sieve to strain out the katsuobushi, and press down on the remaining katsuobushi to extract as much broth as possible.
Boil the buckwheat noodles in boiling water, then remove and rinse in cold water.
Mix the prepared broth concentrate with water in a 1:6 ratio to make the soup, and add ice to keep it chilled.
Place the cooked buckwheat noodles and cold broth into a bowl, and top with the prepared green onion, grated radish, seaweed flakes, and wasabi to finish.