Drain the cooked cauliflower thoroughly in a colander. Let it sit for 5 minutes to allow excess steam and water to escape. Press gently with a spoon to remove more moisture. This step is key for creaminess.
Transfer the drained cauliflower and the cooked garlic to a food processor or a large bowl if using a hand masher.
Add the butter, heavy cream, Parmesan cheese (if using), salt, and pepper to the processor.
Process until the mixture is completely smooth and creamy. Stop occasionally to scrape down the sides. Do not over-process, or it may become gluey.
Taste and adjust seasoning as needed. Serve immediately.
Notes
For the creamiest texture, use a food processor instead of a hand masher.