Cut the cheeks off each mango and chop the flesh into large chunks. Peel onion and cut into quarters. De-seed chilli and chop into chunks.
Add all of the ingredients into a blender. A smaller one is perfect for this to ensure it's completely liquified when blended.
Blend on high until all the ingredients are well combined. This should take less than a minute.
Pour the sauce into a large saucepan and bring to a boil. Reduce the heat and simmer for 10 minutes.
Cool for 5 – 10 minutes then transfer to a large jar or bottles. Store in the fridge where it will keep for a couple of months.