Place the cauliflower, onion, and chicken broth in the pot of your Instant Pot and then lock lid in place. Turn the top valve to “Sealing”.
Press “Manual”, then press “Pressure” until the light on “High Pressure” lights up, then adjust the +/- buttons until time reads 10 minutes.
When the time is up press “Cancel” to stop the cooking and then wait 10 minutes as the Instant Pot does a natural release. After 10 minutes carefully, turn the vent to “Venting” to release the remaining steam.
Remove the lid and add the lemon juice then use an immersion blender to puree the soup until it is smooth and creamy.
Add salt and pepper to taste.
Ladle the cauliflower soup into bowls and top with bacon, chives, sour cream, and cheddar cheese.