Vietnamese Chicken Curry Soup

oil

garlic cloves, finely sliced

small red onion, thickly sliced

lemongrass stalk, white part cut into short lengths

curry powder (preferably Vietnamese curry powder)

chicken stock

(3 cups)boiling water

plus 2 tablespoons) tin of coconut milk

fish sauce

sugar

sea salt

small chicken breast fillets (or 1 large chicken breast fillet)

small sweet potatoes, peeled and cut into large chunks

small handful of water spinach, cut into short lengths

vermicelli noodles

red chillies (optional)

coriander (cilantro), finely chopped

limes, cut into wedges