Instructions: Peel shrimp, reserving shells, and both devein and continue slicing lengthwise, pounding flat - then set aside.

Heat oil in a large saucepan, then fry the shrimp shells in it until they turn pink. Pour in chicken stock and bring to a boil, then reduce and let simmer. Cut the lemon grass stalks in pieces - reserving the bottom 5 inches - then bruise the pieces with a few heavy hits, then toss them into the soup.

Cut the reserved lemon grass into thin pieces, then either toss into a blender or pound with the garlic, the cilantro stems, the chilies, and and lime zest and leaves, and white pepper. Stir into the soup, bring to a boil, then reduce and simmer for 20 minutes.

When the stock is done, pour through a sieve, return to the saucepan, and reheat. When soup is at a boil, add shrimp and mushrooms and cook for 2 to 3 minutes, until the shrimp are pink. Reduce heat, add lime juice and fish sauce, and taste for seasoning.

When ready to serve, stir in slivered chilies and cilantro leaves, then ladle into bowls.

Serve to 4, all at once with rice and any number of other dishes. In a way, it serves as a beverage to the whole meal, served, as it traditionally is, all together.

Comments: This Thai soup is wonderful - hot and sour and piquant, an outstanding combination of rich, chewy shrimp - slippery mushroom - and the foresty green of just cooked cilantro fronds in a complex broth.

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