The polenta will seem very loose initially, but don't worry; it will set up as it sits overnight. In order for the Parmesan to melt and brown nicely on top of the casserole, we found it best to use finely grated fresh Parmesan rather than pre-grated cheese, which has a coarse, granular texture; finely grating the Parmesan is easy to do using the fine holes of a box grater or a Microplane grater.
This recipe is from our cookbook The Best Make-Ahead Recipe.
7 1/2 cups water
2 cups whole milk
1 1/2 cups polenta (9 ounces)
4 tablespoons (1/2 stick) unsalted butter
1 medium garlic clove , minced or pressed through a garlic press (about 1 teaspoon)
Ground black pepper
2 ounces Parmesan cheese , finely grated (about 1 cup, see note)
1. Bring the water and milk to a boil in a partially covered, heavy-bottomed Dutch oven over medium-high heat. Add 1 1/2 teaspoons salt, and very slowly pour the polenta into the boiling liquid while stirring constantly in a circular motion with a wooden spoon (see the illustration below).
2. Reduce to a simmer over low heat and cook, stirring often, until the polenta no longer has a raw cornmeal taste, all of the liquid has been absorbed, and the mixture has a uniformly smooth but very loose consistency, 20 to 25 minutes.
3. Off the heat, stir in the butter and garlic and season with salt and pepper to taste. Pour the polenta into a 13 by 9-inch baking dish. Sprinkle the Parmesan evenly over the top.
4. To Store: Wrap the dish tightly with plastic wrap, poke several vent holes in the plastic, and refrigerate for up to 2 days.
5. To Serve: Adjust an oven rack to the middle position and heat the oven to 450 degrees. Remove the plastic wrap and lightly pat the cheese with paper towels to absorb any condensation that has accumulated. Bake uncovered until the polenta is bubbling and the cheese is nicely browned, 30 to 40 minutes.
To Serve Right Away
Reduce the amount of water to 5 1/2 cups and the amount of milk to 1 cup; cook the polenta until thick and smooth but still pourable, about 30 minutes. Stir in the butter and garlic as described in step 3. You then have two options for serving: 1) Transfer the polenta to a broiler-safe baking dish, sprinkle the Parmesan evenly over the top, and broil until golden browned, 5 to 10 minutes, or 2) Stir the Parmesan directly into the polenta in the saucepan and serve immediately.