One night, on the southern Japanese island of Kyushu, I ordered a bowl of ramen and watched the cook serve a paste alongside the noodle soup that I’d never seen before. It was yuzu kosho. It only has three ingredients: salt, hot pepper, and yuzu, the Japanese citrus, but it’s fascinating. It has spice, fragrance, aroma—everything. There are two types: red, made from ripe yuzu and red chiles, and green, from unripe fruit with green chiles. I use the sharper green version to cut through rich meats, and the milder red in seafood dishes, like these grilled scallops.