Thai Coconut Chicken Soup

2 lemongrass stems, white parts only, or 1 tsp lemon zest
8 small button mushrooms, stems trimmed and quartered
2 chicken breast fillets
4 cups chicken stock
1 inch piece ginger, peeled, cut into matchsticks
2 tsp sugar
1 can coconut milk
1 TBS fish sauce or soy sauce
2 TBS lime juice, plus wedges to serve
2 TBS coarsely chopped mint leaves
2 TBS coarsely chopped basil leaves

Bruise the lemongrass stems with the back of a knife and cut each one in half. Cut the chicken breast into bite size pieces. In a saucepan, bring the chicken stock, lemon grass, ginger, and sugar to a gentle boil over medium high heat. Add the chicken, mushrooms and coconut milk. Simmer without boiling for five minutes, until chicken is cooked. Add fish sauce and lime, mint and basil leaves, serve right away.