Add all of the sauce ingredients except the butter to a food processor and process until smooth.
Put the onion sauce into a separate bowl. If you don't have a food processor, chop the onion finely and mix in the seasonings.
Pierce the skin of the chicken breast with a fork to prevent shrinkage. Sprinkle salt and freshly ground pepper on both sides.
Dust the chicken with katakuriko or flour. Heat oil in a frying pan and cook the chicken until both sides are well browned.
Add the sauce from Step 2 and cook over medium-low heat, covered, for 5-6 minutes until the chicken is cooked through. Add the butter during the last minute of cooking.
Remove the chicken from the pan and cut it in half to make sure it is cooked all the way. Reduce the onion sauce a little.
Cut the chicken into bite-size pieces and top with the reduced onion sauce.
Story Behind this Recipe
I wanted to make a main dish using inexpensive chicken breast.
Cook over high heat until the skin is crispy. The onion sauce is good with all kinds of foods, like white fish, pork, or warm vegetables, so it's convenient to make a big batch and keep it in the refrigerator for 2-3 days. You don't have to add butter. Without the butter, it will have more of a Japanese flavor.