I just made pureed cauliflower the other day to substitute for mashed potatoes. It was really good.
Steamed Cauliflower - 1/2 a head
3 cloves of garlic - steamed with the cauliflower and crushed (I just smash it with the flat side of a knife. It stays whole, but is broken open)
1/2 teaspoon of salt
Butter (I used cream) - I used about 1/3 cup
Toss it all in a food processor and mix til creamy. I'm not going to miss the potatoes.