In a saute' pan, heat oil over medium hight heat. Add the Italian sausage; cook, until brown, about 5 minutes. Reduce the heat to medium. Add the onion, garlic, oregano, rosemary and mushrooms; cook, stirring constantly, for 5 minutes.
Add the tomato paste, chili flakes, diced tomatoes, wine, ½ cup of water, 1/2 teaspoon of salt and ground black pepper. Bring to a boil then simmer, stirring often, until the paste has dissolved, and sauce has thicken, about 10 minutes. Remove from heat.
In a large sauce pot, add polenta, 8 cups of water and 2 tsp of salt. Bring to a boil then reduce the heat to medium low; cook, stirring constantly, until creamy, about 20 minutes. Then add the butter and cook for another 5 minutes. Remove from heat. Stir in 2 tbsp of creme fraiche.
Divide the polenta among plates. Spoon the sauce on top. Sprinkle some parmesan cheese and garnish with basil.