Combine the water, milk, butter, salt, and white pepper in a large saucepan, and bring to a boil over high heat. Whisk in the polenta little by little, and cook, stirring continuously, until the mixture begins to thicken. Then reduce the heat to medium-low and cook, partially covered and stirring frequently, for 30 to 40 minutes, or until the polenta is thick, creamy and tender. If the polenta gets too thick before it is tender, add a bit more water as needed and continue cooking.

Add the Parmesan and the cream, and stir to blend. 

Serve immediately or cover and keep warm until ready to use. (Leftover polenta is easily reheated in a small saucepan with a little water or milk to soften it.)