Thai Chicken Soup (Tom Kha Gai)

This is what I did with turkey leftovers.
1 stalk lemongrass
2 tablespoons vegetable oil
1 medium onion, diced small
1 clove garlic, minced
1 tablespoon Thai red curry paste (Also available at most groceries.)
6 quarter-inch wide slices fresh ginger
3 kaffir lime leaves (Not available at most groceries. I usually substitute ½ teaspoon grated lime peel.)
4 cups chicken stock
2 c. shredded, cooked chicken (or turkey)
2 cups shitake mushrooms, stemmed, caps quartered
1 14-ounce can coconut milk (Don’t use low-fat. Trust me. I tried it.)
Juice of two limes (about five tablespoons)
2 tablespoons nam pla (AKA fish sauce)
3 green onions, trimmed and sliced into ¼ inch pieces
¼ cup chopped fresh cilantro

Trim lemongrass, cut into three pieces about four inches long. Whack the pieces with the flat side of your knife blade to crush slightly.
Heat oil in a saucepan over medium-high heat.
Saute onion and garlic for about two minutes.
Add lemongrass, curry paste, ginger discs, and lime leaf (or peel). Cook, stirring, for three minutes.
Add stock. Bring to a boil. Reduce heat to low and simmer for 15 minutes.
Add coconut milk, cooked chicken and quartered mushroom caps. Cook five minutes.
Add lime juice and nam pla. Taste for balance between nam pla and lime. If one flavor is dominating too much, add a little of the other.
Garnish with green onion and cilantro.