Place one cup of water into the Instant Pot before placing in the trivet that came with the Instant Pot and cauliflower.
Press Manual and set the Instant Pot to 4 minutes. Quick release when done.
Carefully remove the cauliflower, trivet, and drain the water. Let the cauliflower sit and cool for 3-5 minutes.
Cut the cauliflower into quarters or more before adding it back into the Instant Pot (or large bowl). Add in the parmesan, salt, pepper, and butter.
Mash with a potato masher, or blend with a blender/handheld blender, or blend with a food processor until it is your desired consistency. Optional: add a few tbsp of milk, yogurt, or cream cheese to make the mashed cauliflower richer.