Thai Hot & Sour Shrimp Soup

1 tablespoon olive oil
Shells from shrimp (see below)
8 cups chicken stock
3 stalks lemon grass, cut into 1" lengths
4 kaffir lime leaves (can be found in Thai and Chinese markets, often frozen)
1 teaspoon lime zest
2 green Serrano chiles, slivered
2 pounds fresh shrimp, approximately 20 count per pound, shelled and deveined
1 tablespoon coconut milk
1/2 teaspoon salt
juice of 2 limes
1 red Serrano chili, slivered
2 tablespoons coriander leaves (cilantro), coarsely chopped
3 green onions (including some green), coarsely chopped

Heat the oil in a saucepan and fry the shells until they turn pink. Add the chicken stock, lemon grass, lime leaves, lime rind,and green chilis. Bring to a boil, cover, reduce heat and simmer for 20 minutes. Strain the mixture through a sieve, return the liquid to a saucepan and bring to a boil. Add the shrimp to this boiling "stock" and cook them for 2-3 minutes. Reduce heat to simmer and add the coconut milk, salt and lime juice. Stir and immediately remove from heat to prevent overcooking. Pour the soup in a tureen or ladle into bowls, sprinkle with red chilis, coriander leaves and green onions. Serve piping-hot.

From: The Original Thai Cookbook by Jennifer Brennan
Adapted by Patti Vincent