When the pasta is al dente (cooked with a little bit of bite), drain it reserving half a cup of the pasta water.
A very neutral tasting milk is best and it must be unsweetened. I didn't like the results with almond milk as I think the flavour of it came through in the sauce. I tried a few different varieties and my favourite to use for this was soy milk. Silk Coconut Milk & So Delicious Coconut Milk also gave ok results.
Leftover sauce can be stored in a sealed container in the fridge for 4 - 5 days