BRING 4 cups of water to a boil. Whisk in the polenta. Once it begins to thicken, reduce heat to a simmer and cook for 45 minutes until creamy and thick, stirring occasionally to prevent sticking. Stir in the Parmesan and a ¼ teaspoon of salt. Stir until melted and cheese is no longer visible. Remove from heat.
LINE an 8x11 inch baking dish with ALCAN® standard Foil and carefully pour the polenta into the baking dish, using a spatula to smooth it to an even thickness, about ¾ inch. Cover and refrigerate for at least two hours and up to two days until firm.
WHILE the polenta chills, make your ragu. In a large heavy skillet, heat the olive oil over medium heat until simmering. Add the onion and garlic and sauté until fragrant and translucent, about 5 minutes. Stir often to prevent browning. Add mushrooms and thyme and cook over medium-high heat until the mushrooms start to release their liquid. Add ½ teaspoon of salt and continue to cook another 5 minutes until they begin to soften more.
ADD flour, stirring, until it is no longer visible, about 1 minute. Add in the wine, cream and sugar and bring the mixture to a simmer. Taste and adjust salt if desired. Simmer until thick and creamy and the mushrooms are nicely coated, approximately 15 minutes. Finish with a squeeze of fresh lemon juice and ½ cup minced parsley. Set aside and cover to keep warm.
SLICE your polenta into squares — whatever size you desire. Wipe down your skillet, coat it with non-stick cooking spray and heat it over medium-high. Fry the squares in the pan until golden brown and warmed through. To serve, top the squares with warm mushroom ragu.