Add all the ingredients to a food processor, except the salt and also the sugar (if you are making the vegan version) and pulse until smooth.
Put the sauce into a saucepan on medium to high heat and wait for it to slightly boil.
Reduce the heat so that the sauce is simmering and leave for 10-15 minutes, stirring occasionally and until the sauce has reduced to a thick texture.
Leave the sauce to cool, add the pinch of salt (and the sugar at this stage for the vegan version) and then add it back to the food processor or blender. Give it another big whizz round until the sauce is super smooth.
Pour into a jar or bottle and put in in the fridge... Voilà!