Peel potato and cut into small cubes. Soak or double-boil to reduce potassium if you are on a low potassium diet (see helpful hints below).
In a medium-size pot, boil cauliflower and potatoes for 25 minutes. Drain and place in food processor or mixing bowl.
Add margarine, half & half and salt (optional). Process or mix on high speed until smooth. Serve hot.