Preheat the oven to 200°C/180°C fan/. Break the leftover chicken carcass into a few pieces and place onto a large baking tray with the onions, carrot and garlic bulb. Add the sesame oil and toss to coat all the ingredients in the oil
Place the tray into the oven for about 30 - 40 minutes, or until everything is golden and fragrant.
Scrape everything off the tray into a large pot with a lid. If there is anything left on the tray, place the tray over a medium heat and add 100 ml of water - using a wooden spoon to scrape up all of that flavour from the tray. Transfer the flavourful water to the pot along with the roasted chicken and onions.
Add the ginger, spring onions, lemongrass, star anise and white peppercorns to the pot alongside 1.5 litres of cold water, covering all of the contents. Bring the water to a boil and immediately reduce the heat to bring the stock back to a gentle simmer. Simmer partially covered for at least 4 hours, occasionally skimming off any foam that forms on the surface. After 4 hours, you should have an aromatic stock that is rich in colour and flavour. Strain the stock through a fine mesh sieve into a bowl and set aside until needed. The stock can also be frozen at this point.
When you’re ready to cook your soup, add the groundnut oil and garlic cloves to a large high sided saucepan and heat gently until the garlic starts to sizzle and turn a pale golden brown. Strain the garlic and oil through a fine mesh sieve set over a heatproof bowl and set the crispy garlic aside.
Add the garlic infused oil back into the pan along with the chicken stock, soy sauce, fish sauce and bring to the boil.
Add in the rice and mustard greens or spinach and cook for a couple of minutes to warm everything through. Season with the sugar and white pepper - adding more soy sauce or fish sauce to taste and spoon into large bowls. Serve with the crispy garlic chips and the remaining accompaniments to build the rice soup bowls.
Notes
A Thai inspired Rice Soup that provides a surprisingly rich broth even with just one chicken carcass.