Of course, making it at home means I can customize it to my preferences. It's surprisingly easy to make! This recipe is loosely adapted from David Johnson's Thai Food, a brick-sized comprehensive guide to Thai cooking.
Note that you can make a pescatarian version (fish stock, shrimp instead of chicken) or even vegetarian or vegan (veg stock, tofu for chicken, soy sauce for fish sauce) though the latter will lack some of the pungency that only comes with fish sauce.
Step 1: Tools and Ingredients
1 can coconut milk
2-3 cups chicken stock (homemade is best, then the stuff in cartons; boullion cubes are a last resort.)
pinch of salt
1 teaspoon palm sugar (I usually substitute brown sugar)
2 stalks fresh lemongrass, washed and choppped in chunks (dried lemongrass is far inferior - punch it up with extra lime juice and zest at the end if you're forced to go this route)
3 red shallots, peeled and chunked (I often substitute 3 smashed cloves of garlic plus a bit of onion)
2 coriander roots, scraped (I usually substitute a pinch of whole coriander seed plus a handful of fresh coriander (cilantro) leaves)
2 chili peppers, halved (pick your favorite type, and modify number to suit your spice taste)
1.5 inch chunk of galanga root, chunked (ginger is in the same family, but tastes totally different - galanga TOTALLY makes the flavor of this dish. If you can't get this locally, travel to a nearby city and visit the asian markets or scour the internets, buy a pound, then freeze what you can't use now. It's a floral flavor that you'll definitely recognize if you've had tom kha gai before.)
3 kaffir lime leaves, coarsely chopped (I have a kaffir lime tree in my yard, but you can substitute lime zest if necessary. It just won't be as fragrant and complex.)
1 teaspoon chili garlic sauce (optional, and kind of a cheat, but often good.)
1 pound boneless skinless chicken thighs, cut to 1" pieces (you can use breasts, but the thighs are moister and tastier)
1 cup chopped mushrooms (your choice - mix it up)
1-3 Tablespoons fish sauce (This stuff is pungent - if you're not familiar, add incrementally and taste before increasing. But don't be turned off by the smell. Definitely use some, as it's a key flavor that softens when you add it to the soup.)
1 can baby corn, drained and chopped to 1/2" chunks (optional)
1 Tablespoon lime juice (more if compensating - see notes above)
1 handful fresh cilantro, chopped
1/2 cup grape tomatoes halved, or 2 plum tomatoes coarsely chopped (optional)
1 large pot, at least 3 qt
Step 2: Make broth
Step 3: Strain broth
You can usually smoosh more tasty liquid out of the chunks if you try, so give them a stiff squeeze.
Step 4: Add chunks
Step 5: Finish and serve
This soup keeps beautifully, and will taste even better the next day after the flavors mingle overnight. You may want to hit it with a bit more fresh lime after reheating, though, just to keep it zippy.