Put the cashews in a small bowl and pour over enough boiling water to cover. Leave to soak for 15 minutes. Even if you have a high-powered blender it's worth doing this as it makes the sauce extra silky and glossy!
Drain the cashews through a sieve, (discarding the water) and add them to a blender along with all of the other ingredients. Start off with the lowest quantity of milk so that you can adjust to suit your needs.
Blend until completely smooth. Check the consistency and add more milk as necessary, blending for a few seconds between each addition to combine.
Finally taste to check the seasoning and adjust as necessary.
