Add 1" water to a large pan and bring to boil.
Add pinch kosher salt and cauliflower florets.
Cover and cook 8-10 minutes.
When you can spear Cauliflower with fork easily, they are done.
Drain off water, keep cauliflower in pan.
In a medium bowl add sour cream, horseradish, parsley, feta if using, pinch of kosher salt and pepper and stir to combine.
Using a potato masher or back of fork, mash cauliflower.
Dump sour cream sauce into cauliflower.
Stir to mix and taste, then place in serving bowl.
Top with diced chives