Mix Dashi, soy sauce and sugar in a small bowl.

Boil water in a large pot, then add spinach. After 15-30 seconds, remove from heat and drain water.

Cool spinach in running water, and squeeze water out from spinach.

Cut spinach into 2" sections and place in a bowl. Add Dashi sauce mixture and mix well.

Chill or serve right away with a sprinkle of Katsuobuhi.