From America's Test Kitchen Season 8: Asian Take-Out at Home
Replicating the complex flavors of Thai chicken soup at home can be difficult, since it relies on such exotica as galangal, kaffir lime leaves, lemon grass, and bird’s eye chiles. We wanted a plausibly authentic version of Thai chicken soup that could be prepared with more readily available (i.e., supermarket) substitutions.
We started by making a classic version of the soup, then substituting one ingredient at a time. We developed an acceptably rich and definitely chicken-flavored broth by using equal parts chicken broth and coconut milk (adding the coconut milk in two stages: at the beginning and just before serving). We couldn’t fake the flavor of lemon grass, but it proved to be easy enough to find. Our most exciting find was a “magic bullet” substitution: jarred red curry paste includes all the other exotic ingredients we were missing. Just adding a dollop at the very end of cooking and whisking it with pungent fish sauce and tart lime juice allowed all the classic flavors to come through loud and clear.
6-8 as an appetizer, 4 as a main course
If you want a soup with less fat, it is possible to substitute light coconut milk for one or both cans of regular coconut milk. Fresh lemon grass can be omitted, but the soup will lack some complexity. Don't be tempted to use jarred or dried lemon grass-their flavor is characterless. If you want a spicier soup, add more red curry paste to taste. For a more substantial meal, serve the soup over 2 to 3 cups of cooked jasmine rice. The soup can be prepared through step 1 up to one day ahead of time and refrigerated, but it should be completed immediately before serving, as the chicken and mushrooms can easily overcook.