In a medium-size saucepan, bring the milk, 2 cups water and bay leaf to a boil. Season generously with salt, almost to the point of over seasoning. How do you know that you are there? TASTE IT! When it has reached a boil, slowly whisk in the polenta in small sprinkles. Once all of the polenta has been incorporated, reduce the heat to medium and immediately switch over to stirring with a wooden spoon. Cook the polenta until it begins to pull away from the pan, adding water to loosen it up if it becomes too thick.
When the polenta is thoroughly cooked, it should look creamy and not feel gritty on your tongue. Remove it from the heat and stir in the Parmesan and mascarpone.