Thai chicken & mushroom soup (doubled for parties and to store)

2 tsp vegetable oil
6 large shallots
6 stalks lemongrass
16 sprigs cilantro
chopped coarse
2 tbsp fish sauce
2 qt chicken broth
2 cans coconut milk
about 14 ounces, shaken well
2 cans coconut milk
about 14 ounces, 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 (ask the butcher to run the meat through the slicer if possible)
6 tbsp lime juice
from 5-6 limes
2 tsp Thai red curry paste
4 tbsp fish sauce
steamed brown rice
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
I made this soup for friends and family during the 2013 holiday season. Everyone loved it! Processing the lemongrass and shallots is the most time-consuming part, so I now chop it up in a food processor. I'll make this doubled version of the recipe for parties, or I cook half of it at a time for smaller groups. To make the soup a meal, serve it over steamed brown rice.
If needed, kick off the rice cooker.
phase I - develop the soup base
Process the shallots and lemongrass. Because these ultimately get strained from the broth, these need to be chopped just enough to infuse the broth with their flavor. Peel and quarter the shallots, then pulse them in the food processor and transfer into a separate container. Or simply chop them. Remove the tough outer leaves and the bottom 1/2 inch of each lemongrass stalk. Pound the bottom 5 inches of the stalk with the dull part of the knife then cut it into 1-inch pieces. Pulse in the food processor until broken down but not pureed. Or chop them the way Charles Phan would in the notes below.
Warm the oil in a large dutch oven over medium heat. When the oil starts to shimmer, add the shallots, lemongrass, 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 15 minutes.
Working in batches, pour the broth through a fine mesh strainer and discard the solids. Rinse out the pot and transfer the broth back into it. If cooking half of the recipe, transfer in just half of the broth and store the rest in the fridge or freezer.
phase II - cook the soup contents
If cooking half of the recipe, use only half of the ingredients for the following steps. Reserve the other half for the following day.
Warm the strained broth over medium-high heat. Stir in the second can(s) 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, and fish sauce in a small bowl or glass. Stir this mixture into the soup.
serve and garnish
Because I don't like crossing the room with a filled bowl of soup, I ladle the soup into the bowls table side. Place a trivet over the dining table and transfer the pot on top of it. If serving with rice, create a bed of rice at the bottom of each bowl. Ladle the soup over the rice.
Garnish the soup with cilantro, chiles, and scallions. Squeeze in the juice from the lime wedges table side and enjoy immediately.
day 2 (if applicable)
Proceed with the recipe from step 7 and on with the remaining ingredients.
source: adapted and adjusted from the recipe in the January-February 2007 issue of Cook's Illustrated
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.