Rinse shrimp and shell, reserving shells.
Trim both ends of lemongrass stalks and discard the tough outermost layer. Set aside 1 stalk for later.
Take the remaining 3 lemongrass stalks and crush lightly by hitting with the back of a knife. Cut lemongrass into 1 inch pieces.
In a large soup pot combine water, lemongrass, reserved shrimp shells, cilantro stems, salt and pepper. Bring to a boil and simmer, uncovered for 20 minutes. Strain broth into another saucepan.
Thinly slice the lower 6 inches of the remaining lemongrass stalk discarding the rest. Add lemongrass and julienned ginger to the broth, simmer 5 minutes.
Add shrimp and simmer 1 minute until pink and firm to touch.
Cut chile in half and remove seeds. Slice chile so pieces are large enough to easily see.
Add fish sauce, lime juice and chile to soup. Taste for seasoning. Serve soup into 6 bowls.
Add cilantro leaves and lime leaves before serving.