Heat the peanut oil in a large saucepan or skillet over a medium heat. Once hot, add the peanuts, kaffir lime leaves and zest, grated ginger and chillies. Turn the heat to low, and cook for 3-5 minutes until fragrant.
Use a slotted spoon to carefully transfer the peanuts and flavourings (except the kaffir lime leaves – leave those in the pan) to a mortar and pestle. You could potentially use a food processor, but make sure you allow the mixture to cool completely if you intend to do so.
Add the brown sugar to the peanuts in the mortar and pestle, and pound the mixture until most of the peanuts are crushed. You’re looking for the consistency of a very dry crunchy peanut butter.
Return the crushed peanuts to the pan, and turn the heat to medium. Once the peanuts are sizzling again, pour in the coconut milk, and stir thoroughly to combine.
Once combined, add the remaining ingredients except the lime juice, tasting and adjusting as you go. Start with the minimum suggestions, and work your way up to a flavour that suits you. You can also add more chilli sauce (I use Tabasco) if you want an additional chilli hit.