Thai chicken and mushroom broth

1. Put 2 chicken breasts in a pan with a stock cube and cover with cold water. Bring to the boil, then turn off the heat and cover for 15 mins.
Tip the stock into a saucepan, then stir in the curry paste, fish sauce, sugar, lime juice and most of the zest.
Bring to the boil, then add the mushrooms and whites of the spring onion. Cover, then simmer for 2 mins.
Stir in the chicken and most of the spring onion greens to gently heat through, then serve ladled into bowls and scattered with the remaining lime zest.
Serve with extra lime juice, sugar and fish sauce on the side so everyone can adjust their own bowlfuls.