Tentsuyu is commonly known as Japanese tempura dipping sauce, but is actually a common general purpose dipping and simmering sauce used widely in Japanese cuisine.
The recipe for tentsuyu depends heavily on the seasons and the ingredients for which tentsuyu is being prepared. A general, all purpose, tentsuyu might consist of three parts dashi (niboshi dashi, konbu dashi, shiitake dashi, or konbu and katsuobushi dashi), one part mirin, and one part shoyu [Japanese soy sauce]). For ingredients with strong odors or flavors, however, sake and sugar might be used instead of mirin, for example.
Tentsuyu is known as donburi ni shiru ("donburi simmering soup") when used to simmer the ingredients for donburi. It is also used as a hot soup for dishes like agedashi tofu.
