Ponzu

This common, versatile sauce is usually served with grilled fish or vegetables or with shabu-shabu, but it turns up everywhere and can be used in many ways. It keeps indefinitely—a friend of mine insists it’s best after months in the refrigerator; certainly it’s no worse. You can buy yuzu juice frozen or—sometimes—fresh at Japanese specialty markets; it has a unique flavor but close enough to lemon and lime that the combination is a good substitute. You can also get bonito flakes at Japanese markets. If you are serving this as a dipping sauce at the table, garnish with finely chopped scallions or chives.