Set the oven to 400°F/200°C with high fan. Roast the chicken bones and legs on a clean baking tray for about 45 minutes or until nicely browned.
Remove the bones and add to the instant pot. Deglaze the pan with a little water and scrape the golden bits with a wooden spoon. Add this liquid to the instant pot.
With the browned bones in the Instant pot, fill to the max line with cold water and 1 tsp salt. Set on sauté function and bring to a boil (Approx 20 minutes).
While the stock is coming to a boil, wash and peel the carrots and cut in half. Cut the onions in half but leave on the skin. Cut one head of garlic in half and set aside. For the lemongrass, beat it with the back of a knife to release some flavour.
Fry the onions and carrots in 1 tsp of vegetable oil until golden brown.
Once the stock has come to a boil, immediately skim off the fat and scum.
Add the browned vegetables and the rest of the ingredients to the instant pot.
Double check that the Instant pot is not filled higher than the max line. Fill with more water or remove water so that the water level is at the max level line.Close the lid and set the timer for 2 hours at high pressure.
Once the timer goes off, turn off the instant pot and let it naturally depressurize for 30 minutes.
After waiting 30 minutes, quick release the rest of the pressure.
Once all the pressure has been released, open the lid and strain the stock using a spider strainer and then a fine mesh strainer. Save the cooked chicken meat for later.
Bring the stock to a boil in another pan and simmer for 5 minutes to concentrate the flavour. Check the seasoning and add more salt if you wish.
To serve, add some of the cooked chicken to a bowl and season with a little salt and pepper. Pour the hot broth over and serve right away. Enjoy!