Use your hands and the small, sharp knife to separate the cauliflower into florets and chop the stem fine. (“Florets” are the branched clusters at the top of the cauliflower.) Throw away the tough inner core.
Put the pot on the stove, add the cauliflower and water, and bring to a boil over high heat(Setting 6). (You’ll know the water is boiling when you see bubbles breaking all over its surface.) Cover and turn the heat down to low.
Cook the cauliflower until very tender, 15 to 35 minutes depending on the size of the cauliflower florets. If there is liquid left in the pot, drain the cauliflower in the colander and return it to the pot.
Mash, using a potato masher or fork, or blend with a handheld blender or food processor.
Add the olive oil, yogurt and, if using, butter, salt, and pepper and mash until smooth. Serve right away, or cover and refrigerate up to 2 days.
