Ponzu, a citrus-based Japanese dipping sauce is traditionally made using yuzu, a tart Japanese citrus fruit. While some Americanized recipes use combinations of limes, lemons, and oranges, you can often find yuzu at San Diego farmers markets or at Asian supermarkets. Though you can buy premade ponzu at international markets, making your own is easy, and ensures you know exactly what's in your sauce.
Combine mirin, rice wine vinegar, soy sauce, and bonito flakes in saucepan and bring to a boil. Remove from heat and cool to room temperature.
Strain out bonito flakes and mix in yuzu or lime juice.
Serve immediately alongside pan-fried gyoza, use as a tangy marinade, or sprinkle over your strifry for a nice punch of tangy umami.
Refrigerate leftover ponzu in an airtight container and enjoy within 5 days.