Remove the heads and guts from the dried sardines. Place sardines, kelp, and water in a pot and let sit for 30 minutes.

Slice carrot, zucchini, shiitake mushrooms, and green onion thinly.

Wash clams by rubbing them together in water and drain.

Heat the pot with the broth ingredients over low heat. Remove kelp when small bubbles appear. Skim off any foam and simmer for 5 minutes. Strain the broth through a sieve lined with kitchen paper.

Return the strained broth to the pot. Add clams and simmer over medium-low heat until clams open, about 3–4 minutes. Remove clams and set aside. Add sliced vegetables and soy sauce to the broth and simmer for 5 minutes. Season with salt.

Return clams to the pot and bring to a boil.