Cut cauliflower into florets, discarding leaves and thick stem. (Don’t make them too small.)
Place the wire rack that came with the Instant Pot at the bottom of the pot. Add 1 cup of water to the bottom.
Add cauliflower florets on top of the rack. Add garlic cloves, salt, and pepper.
Close the lid and make sure to turn the valve to “seal.”
Set to Pressure Cook on high for 7 minutes. Once time is up, let it do a natural release for 10 minutes and then you can finish with a quick release.
Transfer cooked cauliflower and garlic cloves into either a mash vegetable bag or doubled cheese cloth to be squeezed. (You may been to let it cool.) Squeeze most of the liquid out of cauliflower so that mashed cauliflower is not runny.
Transfer squeezed cauliflower and garlic into a food processor. Add milk and butter. Pulse until all smooth. You may need to add a little more milk, depending on how much liquid was squeezed out of the cauliflower.