Hubby and I tried this the other night. Obviously it isn't quite like regular mashed potatoes, but it was tasty. I made a modification, though. Instead of adding in some butter, I added in some fat-free half and half. I put in a splash, and kept adding a little bit at a time until it was the right consistency.
Cook a bag of microwaveable pre-cut cauliflower as directed on the bag.
*Then put it into a food processor or blender with half a tablespoon of butter, a pinch of garlic powder,a pinch of onion powder, and salt and pepper to taste.
*If want it to be thicker you can dry the cauliflower with a paper towel before you blend it.
Cauliflower is very low in calories, so you can afford to use a small amount of butter.