Remove the shrimp shell but leave the tails (for look). Then cut open the back of each shrimp to remove the veins. Clean the mushrooms with water and dry them well before wedging each into quarters. Bring water to boil, then add lemon grass, lime leaves, and shrimps. When the shrimps turn pink, add mushrooms and salts. Remove the pot from heat after boil. Add fishsauce, lime juice, and hot peppers to taste.
Serve the soup while still hot in individual soup cups and top each cup with pieces of cilantro.