Cut the onion in half, roughly chop one half and finely slice the other.

Pound lemongrass stalks with the blunt edge of a knife to soften and release the flavour, then chop roughly.

Chop three chillies roughly and finely slice the other two.

Add the water to a large, heavy-based pot, put on a medium heat then add the chicken, lemongrass, roughly chopped onion, corn cobs (keep kernels aside), roughly chopped coriander stalks and roots, roughly chopped chillies, ginger, fish sauce, sesame oil and soy sauce.

Bring to a low simmer and cook for an hour. Add coconut milk and bring back to a low simmer.

Cook until chicken is soft (a further 30 minutes to an hour), making sure the meat remains submerged.

Remove chicken and cool a little before picking off the meat.

Strain stock, return it to the pot and keep it hot.

Finely slice green onions, reserving white stalks for the salad.

In a medium-sized bowl, mix the corn kernels, sliced green onion, roughly chopped coriander leaves, finely sliced chillies and onion, and chicken meat.

Divide the mix between four serving bowls, top up with hot chicken broth and serve immediately.