In a large saucepan, bring the water, milk and butter to a boil. Add 2 teaspoons of salt to the water and whisk in the polenta. Whisk constantly for 3 to 4 minutes to prevent lumps. Simmer for 45 minutes, partially covered and stirring every 10 minutes, until the polenta is thick, smooth, and creamy. Add the creme fraiche and Parmesan. Check for seasoning and adjust consistency by adding milk or water to the polenta. Polenta may be made up to 20 minutes ahead of time and kept covered until ready to serve.