Cut the onion in half and place it cut-side down in a dry frying pan over medium heat. Let it cook for about 8 minutes until nicely browned. Don’t panic if it looks a little burnt — that’s flavour, baby.
While that’s happening, chop the leeks, carrots, celery, and lemongrass into chunky pieces. Crush the peppercorns with the back of a spoon, then peel and slice the ginger.
Heat the oil in a big soup pot and fry the turmeric for 30 seconds until fragrant. Add the chicken and water, then bring everything to a boil. Scoop off any foam floating around on top.
Toss in the veggies, pepper, thyme, bay leaves, half the lemongrass, and half the ginger. Lower the heat and let it gently simmer away for 2 hours. Give it the occasional skim if needed.
Remove the chicken and strain the broth. Let it cool a little, then pop it in the fridge so the fat firms up on top. Once chilled, scoop the fat off with a spoon.
Pull the meat off the chicken and save it for soups, salads, pasta, wraps — future you will be very smug about this.
Put the broth back on the heat. Add the remaining ginger and lemongrass, then simmer for another 45 minutes on low.
Remove the ginger and lemongrass before serving. Or let the broth cool completely and freeze for a rainy day.