Tom Yum Broth

Combine the water or shrimp stock with the bruised lemongrass, sliced galangal, and torn kaffir lime leaves in a medium saucepan. Bring to a full boil over high heat, then reduce to a vigorous simmer. Simmer uncovered for 10 minutes, pressing the aromatics down into the liquid with a spoon every few minutes. The liquid will reduce slightly and, more importantly, it will extract the volatile aromatic oils from the lemongrass, galangal, and kaffir lime. After 10 minutes, the broth should smell powerfully of the three aromatics — the lemon-citrus of lemongrass, the camphor-hot of galangal, and the distinct floral-citrus of kaffir lime. If your water is very soft, the flavors will be more pronounced; hard water slightly mutes the aromatics. Do not strain yet — the aromatics continue to flavor the broth through the next steps.

Add the lightly bruised bird chilies and the nam prik pao (roasted chili paste) to the simmering aromatic stock. The nam prik pao is the differentiator between tom yum nam sai (clear, pale broth) and tom yum nam khon (cloudy, richer, darker broth) — this recipe uses it for depth and color. Stir until the paste dissolves into the broth — it will turn the stock a warm amber-orange. Add the torn mushrooms and simmer for 3 minutes until softened. Taste the broth now — before adding the shrimp, fish sauce, or lime — and check that the chili heat is at your desired level. At this stage you can add more bruised chilies. The mushrooms will add an umami depth that bridges the gap between the sharp aromatics and the seafood.

Bring the broth to a full rolling boil. Add the shrimp and cook for exactly 2 to 3 minutes, watching closely — shrimp in a hot broth cook far faster than expected. Remove the pot from heat the moment the shrimp are pink and curled into a relaxed C. Off heat, add the fish sauce and lime juice — never boil these after adding. The lime especially must not be cooked further or its bright top note becomes flat and bitter. Add the optional sugar now if the broth needs rounding. Taste for balance: tom yum should be aggressively sour and hot with a deep salty backbone and mild sweetness at the very end. Correct if needed. Ladle into bowls, leaving the aromatic pieces in the bowl (they are decorative and continue to aroma, but are not eaten), and scatter cilantro over the surface.