To a skillet or saucepan, add the dashi (or substitute), onions, soy sauce, mirin, sake, and sugar. Bring up to a good simmer and simmer for about 8 minutes or so until onions are just tender but still holding their shape.

Add the beef, separating as you add, and continue to simmer, stirring, until beef is nearly done to taste. Keep in mind that the beef will continue to cook in the hot broth even after the heat is off.  Total cook time for the beef should be two to three minutes.

Serve over rice, garnished with your choice of any or all of the above garnishes.