Place the salt into the TM bowl and mix on Speed 10 for 5 seconds.
Scrape down the sides of the bowl.
Add the water and cream of tartar and cook for 5 minutes, 60 degrees, Speed 3.
Leave to cool for 5 minutes.
Add the plain flour and the oil and mix together for 50 seconds, Speed 4.
Knead for 1 minute on Interval Speed.
Check the texture and if it's a little sticky, add some more flour and knead for a further 30 seconds.
Separate the playdough into several bowls if making different colours (if you're only making one colour, leave the playdough in the Thermomix, add 1-2 drops of food colouring and mix on Interval/Kneading Function for 1-2 minutes).
In the bowls of playdough, add 1 tiny drop of food colouring (and a sprinkle of glitter - optional) to each bowl and mix together with your hands until the colour is evenly dispersed (wear gloves!).
Store the playdough in sealable plastic bags at room temperature for up to 3 months.