Low carb, very tasty and super easy to make. Just break apart one whole head of cauliflower and steam until soft. Then throw into a food processor, add butter, cream and salt (or whatever you'd normally add to mashed potatoes) and serve! The mouth feel is excellent and you will love the taste.
And by the way, cauliflower also makes a great rice substitute! Very lightly steam, then throw into a food processor and blend until it resembles rice texture, then saute in a pan with oil.