Heat the oil in a large, deep pan, then
fry the onions, ginger, garlic and chilli for
10-15 mins until soft. Add the remaining
ingredients and some seasoning, then boil
for 30 mins, stirring occasionally, until the
mixture has thickened and is sticky.
Cool slightly, then whizz in a blender or
food processor until smooth. If the sauce is
a bit thick for your liking, stir in a dribble of
boiling water. Sieve, then funnel into a bottle
or jar while still hot. Cool completely before
serving. Will keep for 3 months in the fridge.