Melt the butter in a medium saucepan over medium heat. Add the water and 2 teaspoons salt and bring to a vigorous boil over high heat. Add the cauliflower florets, return to a boil, and cook until the cauliflower is very tender, 10 to 12 minutes. Remove from the heat and strain the cauliflower; reserve cooking liquid separately. Place the cauliflower into a blender and add just enough of the cooking liquid to form a smooth puree, usually about 3 tablespoons. Cover the blender tightly (use a kitchen towel to cover lid, pressing down so that it doesn't splatter when the blender is turned on.) Process on very low speed at first, then gradually increase the speed to the highest speed on your blender. Process until completely smooth, light, and airy, usually 2 to 3 minutes. Adjust the thickness by adding more of the cooking liquid if necessary, and add additional salt to taste if necessary. Season with the white pepper to taste. 

When you are ready to serve the puree, rewarm gently in a small saucepan over low heat and use as desired.

Note:  Any remaining puree can be made into a delicious soup just by adding more of the cooking liquid.