In a small sauce pan, gently boil the soy sauce, sake and mirin until reduced by half.
Cool the tare.
Make the onigiri
Measure two tablespoons of tare and stir into the cooked Japanese rice.
Brush the inside of the onigiri mold with a little water (this prevents the rice from sticking to the mold).
Fill the onigiri mold with the seasoned rice then position the cover and press to make the rice compact.
Unmold the onigiri.
Repeat until all the seasoned rice have been shaped.
Pan grill the onigiri
With the stove set to medium heat, brush the bottom of a frying pan with cooking oil.
Lay your onigiri, triangular side down (or the side with the largest flat surface, if your onigiri is not triangular), in the hot oil and cook until the underside forms a light crust. Turn the onigiri over to allow the opposite side to form a crust.
Brush the top of the onigiri (the one where a crust has already formed) with tare.
Flip the onigiri and brush the opposite side with tare.
Turn the onigiri one last time and place a sliver of butter on top.
Repeat with the rest of the onigiri.
Notes
Thanks to Marc Matsumoto for the butter tip.Updated from a post originally published in March 10, 2021