This recipe is a two-part process: first, cooking the creamy polenta, and second, chilling and baking it into crispy squares. Follow these steps carefully for perfect results every time.

Part 1: Cooking the Creamy Polenta Base

1. Prepare Your Pan: Lightly grease a 9×13 inch baking pan or dish with butter or non-stick spray. This will prevent the polenta from sticking and ensure it releases cleanly after chilling.
2. Boil the Liquid: In a large, heavy-bottomed pot or Dutch oven, bring your 6 cups of water or broth to a rolling boil over medium-high heat. Season it generously with the 2 teaspoons of kosher salt. Seasoning the liquid at this stage ensures the flavor is absorbed evenly into every grain of cornmeal.
3. Whisk in the Polenta: Once the liquid is boiling, reduce the heat to low. While whisking continuously and vigorously with one hand, slowly pour the cornmeal into the pot in a thin, steady stream with the other hand. This slow-and-steady method is the secret to preventing lumps. Do not dump the polenta in all at once.
4. Cook and Stir: Continue to whisk for another 1-2 minutes until the polenta begins to thicken. Switch from a whisk to a wooden spoon or spatula. Reduce the heat to the lowest possible setting and cover the pot.
5. The Low and Slow Simmer: Let the polenta cook for 35-45 minutes, stirring thoroughly every 10 minutes. This low-and-slow cooking process allows the cornmeal grains to fully hydrate and become tender, resulting in a supremely creamy texture. Be sure to scrape the bottom and corners of the pot when you stir to prevent scorching. The polenta is done when it is very thick, pulls away from the sides of the pot as you stir, and the individual grains are soft with no grittiness.
6. Add the Flavor: Remove the pot from the heat. Immediately stir in the grated Parmesan cheese, unsalted butter, chopped fresh rosemary, and black pepper. Stir vigorously until the butter and cheese are completely melted and incorporated, and the polenta is smooth and glossy. Taste and adjust seasoning if necessary.

Part 2: Chilling, Slicing, and Baking the Squares

1. Spread and Chill: Immediately pour the hot polenta into your prepared 9×13 inch pan. Working quickly, use a spatula (lightly moistened with water to prevent sticking) to spread it into an even, smooth layer.
2. The Crucial Chill: Cover the pan with plastic wrap, pressing it directly onto the surface of the polenta to prevent a skin from forming. Refrigerate for a minimum of 3 hours, but preferably overnight. This chilling step is non-negotiable; it allows the polenta to become completely firm, which is essential for cutting clean squares.
3. Preheat and Prepare: When you are ready to bake, preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper for easy cleanup.
4. Cut the Squares: Run a knife around the edge of the baking dish to loosen the chilled polenta. Carefully invert the slab of polenta onto a large cutting board. Using a sharp knife or a bench scraper, cut the polenta into your desired shape. For classic squares, you can cut it into 24-30 even pieces (e.g., 4 rows by 6 rows). You can also cut it into rectangles, triangles, or even use cookie cutters for fun shapes.
5. Bake to Golden Perfection: Arrange the polenta squares in a single layer on the prepared baking sheet, leaving a little space between each one to allow for even browning. Brush the tops of the squares generously with the olive oil.
6. Bake: Place the baking sheet in the preheated oven and bake for 30-40 minutes, flipping the squares halfway through the baking time. The squares are done when they are deeply golden-brown, crisp on the edges, and heated through.
7. Serve Hot: Remove from the oven and serve immediately while they are at their crispy, creamy best.