Wash and chop cauliflower into florets. Steam in a steamer basket or in a covered pan with 1/4" of boiling water until soft (about 6 minutes).
Drain cauliflower very well and add to food processor with goat cheese and seasonings. Add Parmesan cheese if using.
Puree until texture resembles mashed potatoes.
Serve with butter and garnish with chives if desired.
Notes
As an alternative to steaming, you can boil the cauliflower, but you will need to drain it well and make sure you've removed as much water as possible before processing.