In a saucepan, bring to a boil the chicken stock, water, milk, garlic, rosemary and salt. Gradually whisk in polenta, set heat to medium-low, and simmer the polenta mixture until thick and creamy, stirring often to prevent lumps, about 15 minutes. Remove from the heat, and stir in the parmesan cheese until well combined.
Preheat oven to 190 degrees C. Grease a 2-litre baking dish. Spoon the polenta into the dish, adding more parmesan cheese if desired. Sprinkle the top with salt and pepper.
Bake in the preheated oven until the polenta is bubbling and golden brown on top, about 30 minutes.