Add water to a large saucier or saucepan and set over high heat. Sprinkle in cornmeal while whisking.

Bring to a boil, stirring frequently. Let boil, stirring frequently, until polenta thickens and starts to spit.

Lower heat immediately to prevent spitting and cook, stirring frequently and scraping bottom to prevent scorching, until thick and pulling away from sides (~50 min). Season with salt to taste.

Stir in olive oil until fully incorporated and no lumps remain. Spread polenta on a baking sheet and chill in fridge at least 1 hour (or overnight).

Process mushrooms in batches in food processor until finely chopped (almost pureed). Scrape sides as needed.

Heat olive oil in a large Dutch oven over medium-high heat. Add onions, season with salt, and cook until soft and slightly caramelized.

Add tomato paste and red chili flakes; cook 5–10 minutes, stirring, until paste caramelizes lightly (don’t burn).

Add chopped mushrooms and cook 30 minutes, stirring occasionally, until liquid cooks off and mushrooms darken.

Add white wine to deglaze; scrape bottom and cook until wine evaporates.

Stir in heavy cream and simmer 10 minutes. Taste and adjust seasoning.

Remove polenta from fridge and cut into 3x3 inch squares.

Heat 2–3 tablespoon olive oil in a pan over medium heat. Sear polenta squares until golden brown on all sides.

Plate mushroom ragu and top with crispy polenta cake. Garnish with shaved ricotta salata and Parmesan if desired. Serve immediately.