Wash the pandan leaves thoroughly, even if they are frozen. There will be dirt in the folds.
Place into the Thermomix bowl with the water and blend 2 min/speed 10. Strain out solids with both a sieve and then nut milk bag and rinse out the Thermomix bowl.
Return the liquid to the bowl with salt, vanilla and sugar and cook 5 min/Varoma/speed 4/spatter guard. If you wish to leave the sugar out, by all means do so.
Store in a sterilized jar in the fridge for up to a week. It will separate, so it is best to give it a good shake prior to use.