Pour milk into your Instapot and place the lid on with the top set to "Venting."
Hit the "Yogurt" button twice. The display should read "Boil." Allow the Instapot to boil your milk. This will take approximately 30-45 minutes. When the Instapot is finished, it will beep and the display will change to "Yogt."
Remove the lid and check the temperature with a food thermometer. The milk should be 180 degrees. If the milk is lower than 180 degrees, close the lid and press the "Yogurt" button twice to boil the milk more. Check again after 10 minutes.
If your milk is at 180 degrees, you can choose to boil it for 5 more minutes to get a firmer set. If you choose not to boil the milk again, you will get a softer, European-style set. To boil the milk a second time, close the lid, press "Yogurt" twice. The display will say "boil" again. Set a timer for five minutes and end the process when the timer beeps.
Remove the inner pot from your Instapot and allow it cool on the counter. When the temperature reaches 116 degrees, you're ready for the next step.
There will be a thin layer of milk skin on the top. Gently remove it with a spatula.
In a small bowl, place the 2 Tbsp of plain yogurt. Add 1/2 cup of warm milk and whisk to combine.
Pour the contents of the small bowl into the rest of the milk and whisk to combine.
Return the inner pot to the Instapot and close the lid. Press the "Yogurt" button once. Program the pot for anywhere between 8 and 12 hours. The longer you leave the yogurt to incubate, the tangier it will be.
Begin checking your yogurt every hour after 4 hours of incubation. Your yogurt is done when you can insert a spoon into the pot and it will remain standing on its own. You can continue to incubate the yogurt after this time for tangier yogurt.
Remove the inner pot and place on the counter. Cover the yogurt and allow to cool to room temperature. Once the yogurt is cooled, stir it, then place it in airtight containers and refrigerate!