Swish some boiling water around the Instant Pot inner and place into the pot, adding 2 ltrs milk. Affix lid and set to vent.
Press 'yoghurt' button on Instant Pot until 'boil' is displayed (should take three presses).
When heating point is reached and the Instant Pot as beeped (after about half an hour), the milk will be hot and just under simmering (it will not be 'boiling'). Check temperature with thermometer if unsure - it should be 84℃. If it isn't at the desired temperature, set IP to 'sauté) and manually bring to temperature, then turn off.
Leave to cool on the counter, uncovered, until temperature is under 45℃
Add 2tbsp live yoghurt to a bowl. Add a ladle of the warm milk to the yoghurt and mix to combine well. Tip this back into the Instant pot and mix thoroughly to distribute. Affix lid and set to vent.
Press 'Yoghurt' function on IP until '8:00' is displayed, for a cook time of 8 hours, then leave to work.
After 8 hours, turn off instant pot and remove the inner pot to cool. Once cool, cover with a clean cloth and place in the fridge overnight.
In the morning, whisk briefly to smooth.
Place a cheesecloth or muslin in a sieve over a bowl, and ladle in some yoghurt. Leave for 2+ hours to drain some of the whey from the yoghurt (which can be saved for use in baking).
Save 2-3 tbsp of yoghurt to serve as the starter for the next yoghurt batch. The starter can be frozen and defrosted if necessary.