1 bunch spinach, trimmed, washed, parboiled
1 1/4 c. dashi
1 tsp mirin
3 tsp light soy sauce
1/3 c. ito-kezuri-katsuo (dried bonito thread-shavings) or regular hana-katsuo (flakes)
Bring dashi to a boil, then simmer. Add salt, mirin, soy sauce. Force-cool by putting it in a bowl inside a bowl of ice. Add spinach and mix, refrigerate 5-6 hours. Serve spinach, with stock poured over, and garnish with bonito flakes/threads.
Source: Japanese Cooking, a Simple Art, by Shizuo Tsuji, p. 430-431