Ponzu is a citrusy Japanase sauce used as a condiment for a variety of dishes such as shabu shabu and some kinds of sashimi. I use it in my crispy steamed chicken with summer vegetables. You can buy readymade ponzu in stores but I prefer to make my own with this recipe courtesy of Donguri's Chef Yorinobu Yamasaki. It makes more than you'll need, but it keeps well in the fridge for months. Note that it should rest in the fridge for 2 days before it's ready to strain and serve.
Briefly bring 1½ Tbsp sake to a boil in your smallest saucepan (or use the micro wave) to rid it of alcohol and pour in a mixing bowl.
1 cup soy sauce
1 cup yuzu juice (available in Japanese grocery stores or online, or substitute with rice wine vinegar)
¾ Tbsp tamari
1" x 1½" piece of kombu
½ cup shaved katsuobushi ("bonito"), ½ oz in weight
1 pinch red pepper flakes
Let the flavors come together in the fridge for 2 days. Strain with a fine mesh sieve. Refridgerate until use.