cook's illustrated thai chicken soup (doubled for parties and to store)

2 tsp vegetable oil
6 stalks lemongrass
processed per notes below
6 large shallots
16 sprigs cilantro
chopped coarse
2 tbsp fish sauce
2 qt chicken broth
1 can coconut milk
about 14 ounces, preferably Chaokoh brand, shaken well
1 can coconut milk
about 14 ounces, preferably Chaokoh brand, shaken well
2 tbsp sugar
1 lb white mushrooms
cleaned, stems trimmed, cut into 1/4-inch slices
2 lbs skinless chicken breasts
halved lengthwise, then cut at a bias into 1/8" pieces
6 tbsp lime juice
from 5-6 limes
2 tsp Thai red curry paste
4 tbsp fish sauce
1 cup cilantro leaves
4 whole serrano chiles
or thai chiles, sliced thin
4 whole scallions
sliced thin on a bias
2 whole limes
cut into wedges
We made this soup for friends and family during the 2013 holiday season. Everyone loved it! Processing the lemongrass and shallots felt like the most time-consuming part, so next time we will try chopping it all up in a food processor. Adapted and adjusted from the base recipe published in the January-February 2007 issue of Cook's Illustrated.
phase I - develop the soup base
Warm the oil in a large dutch oven over medium heat. When the oil starts to shimmer, add the lemongrass, shallots, cilantro, and fish sauce. Cook and stir frequently for about 4-6 minutes until the vegetables are softened but not browned.
Add the chicken broth and coconut milk. Bring to a simmer over high heat, then reduce the heat to low and cover. Simmer for about 10-12 minutes.
Pour the broth through a fine mesh strainer and discard the solids. Rinse out the pot and transfer the broth back into it. Pause and chill (or even freeze) the broth at this point if preparing in advance. Otherwise continue on to phase II.
phase II - cook the soup contents
Warm the broth over medium-high heat. Stir in the second can of coconut milk and sugar and bring to a simmer.
Bump the heat down to medium. Add the mushrooms and cook for 2-3 minutes until tender.
Add the chicken and cook for 1-3 minutes. Stir constantly.
Transfer the soup away from the heat once all the pink from the chicken has disappeared.
Whisk together the lime juice, curry paste, fish sauce in a small bowl or glass. Stir this mixture into the soup.
garnish & serve
Serve the soup and garnish with cilantro, chiles, and scallions. Squeeze in the juice from the lime wedge table side and enjoy immediately.
source: Cook's Illustrated Jan-Feb 2007 issue
These lemongrass handling tips are from page 117 of Charles Phan's Vietnamese Home Cooking cookbook:

Cut the bottom 1/2 inch off each stalk and trim the greenish-woody to portion and discard. Peel the outer layers from the stalk until you arrive at the firm, tender center. Thinly slice the stalk into coins with a sharp knife, then run your knife through the coin until you have reduced them to nubby bits. Processing the lemongrass this way makes the lemongrass register on your tongue, then dissolve, leaving behind the aroma.

Chop lemongrass JUST prior to using. Freeze whole stalks if needed for storage.

However, our friend Elim also taught us to pound the lemongrass with the flat side of the knife blade, then chop it from there.