Chop cauliflower into florets. Peel parsnips and carrots, and chop them into 1/2 inch pieces. Add cauliflower, parsnips, and carrots into a medium size pot and covercompletely with water. Boil until carrots and parsnips are soft (about 10 minutes). Drain cauliflower, parsnips, and carrots mix. Puree in food processor. When the vegetable mix is mostly smooth in the food processor, slowly add oil, milk, salt, and butter, and continue to process. Add the grated cheese, and mix to melt.