In a small bowl combine 1 cup of milk and 2 tbsp of yogurt. Whisk very well until completely smooth.
Add the yogurt mixture and the rest of the milk to the insert of the Instant Pot. If adding creamer or sweetened condensed milk, do so now.
Use a glass Instant Pot lid, or the pressure cooker lid (ring removed) set to "venting".
Press yogurt>normal pressure>8 hours. The time will start to count up (most Instant Pot recipes count down).
When it has finished fermenting, remove the insert from the Instant Pot and place covered in the fridge for 6-8 hours.
For true Greek-style yogurt, strain through a wire mesh strainer lined with a clean thin cloth for 2-8 hours in the fridge.
Notes
Store in the fridge for up to two weeks.To sweeten: use some or all of a can of sweetened condensed milk or up to 16 oz of ultra-pasteurized flavored coffee creamer.You can halve this recipe or double it (as long as it doesn't go above the max fill line). The fermenting time remains the same no matter how much milk you're using.