In 4-quart pot, heat 2 tablespoons oil. Add shrimp and stir-fry briefly until pink but not done. Remove shrimp and reserve. Add tablespoon oil and stir-fry shells until pink. Add stock and water, lime leaves, lemon grass, and 1 tablespoon fish sauce. Bring to boil. Reduce heat and simmer 20 minutes, covered. Strain broth and set aside until ready to serve. Discard shrimp shells but save lemon grass and lime leaves to serve in soup. TO ASSEMBLE SOUP: Add mushrooms to broth (if using straw nushrooms drain them first) and simmer until done,about 5 minutes. Add shrimp and simmer briefly until done (DO NOT OVERCOOK). Just before serving, add fish sauce, lime juice, and chillies, garnish with coriander leaves and scallions. Notes: Khaffir lime leaves, lemon grass, fish sauce, fresh coriander, and Thai birdseye chillies are available in Asian grocery stores. Use any fresh hot chili if unable to find the Thai ones. Although the lime leaves and lemon grass are returned to the soup for serving, they are flavorings only and are not eaten. Use zest of about 1/2 lemon if unable to find lemon grass. If you can find shrimp with the heads on, fry the heads as well as the tail shells for a richer broth. Discard with shells. From The Cookie Ladys Files File ftp://ftp.idiscover.co.uk/pub/food/mealmaster/recipes/mmdja006.zip