Tom yum is a classic Thai soup that is spicy, sour and savory. It also is intensely fragrant and flavorful with Southeast Asian aromatics, including lemon grass, galangal and makrut lime leaves. On a recent trip to Bangkok, we learned to make tom yum gai—the chicken version—from home cook and food blogger Rawadee Yenchujit. Back home, we needed to substitute ginger and lime zest for the harder-to-find galangal and makrut lime leaves. If you can find fresh galangal, use an equal amount in place of the ginger. And if you’re able to get fresh makrut, use 10 sets of leaves (they grow in pairs) in place of the lime zest. The chili paste, sometimes referred to as chili “jam”—nam prik pao in Thai—is a common addition to tom yum. Made by blending shallots, garlic, dried chilies, shrimp paste, tamarind, oil and other ingredients, the paste brings added complexity and color to the soup, along with a touch of fat that helps carry the flavors. Thai Kitchen roasted chili paste is sold in small jars in the international aisle of most supermarkets. If you like, serve the soup with steamed jasmine rice.