Bring water, olive oil, and milk to a boil in 4-quart sauce pan. Add polenta in a thin stream, stirring constantly with a whisk. Lower heat and cook while stirring until polenta is thick as porridge, about 5 to 7 minutes.
Remove from heat and whisk in ricotta evenly through polenta then fold in mozzarella and fontina; cheeses will begin to melt. Season with salt and pepper.
Butter an 8x12-inch casserole or gratin dish evenly. Pour hot polenta into casserole and spread evenly with a spatula. Sprinkle grated Parmesan cheese evenly across top of polenta. Place in oven on broiler setting on middle rack and bake for 3 to 5 minutes, or until top of polenta is golden brown. Remove from oven, set aside for 5 to 7 minutes and then serve. Letting polenta rest will allow cheese to melt evenly inside casserole, which also needs to cool down because of it being so hot.