Step 1

In a large soup pot combine the chicken stock, coconut milk, ginger, lemongrass, curry paste, sugar and onion and bring to a boil

Step 2

Add the chicken, mushrooms and fish sauce

Step 3

Reduce the heat to medium, and simmer until the chicken is white and firm, about 4 minutes

Step 4

Add the salt, lime juice, lime zest and basil and heat to just below boiling, about 3 minutes

Step 5

Serve soup with white rice, additional basil and chili paste if desired.