Tosa Soy Sauce is Japanese soy sauce with shaved bonito and kelp added to it.
It has a stronger, fuller flavour than regular soy sauce.
1/2 cup (4 oz / 125 ml) regular soy sauce
2 tablespoons mirin
4 tablespoons shaved bonito
Mix soy sauce and mirin in a saucepan, heat to boiling. Add bonito; boil for 1 minute. Strain, allow to cool.
Tosa Soy Sauce is named for the province of Tosa in Kochi prefecture in Japan. Tosa was known for its shaved bonito, so any food item with the word “tosa” in it can be expected to have something to do with shaved bonito.