How to Make It
Heat the olive oil in a large skillet. Add the onion and cook over moderately low heat until translucent, about 8 minutes. Add the tomatoes, red wine, balsamic vinegar, tomato paste, sugar, oregano and crushed pepper; season with salt and pepper. Simmer the ragout until it thickens slightly, about 10 minutes.
Meanwhile, in a large skillet, cook the sausages in 1 cup of the water over moderately high heat, turning occasionally, until cooked through, about 12 minutes. Transfer to a cutting board and thickly slice crosswise on the diagonal, then stir into the ragout with the olives. Keep warm.
In a large saucepan, bring the remaining 6 cups of water to a boil with 2 teaspoons of salt. Add the polenta and cook, stirring, until thick, 1 to 2 minutes. Remove from the heat and stir in the butter, rosemary and 1/2 cup of the cheese; season with salt and pepper. Transfer the polenta to a large platter and make a well in the center. Ladle the sausage ragout into the well, garnish with the remaining 1/4 cup of cheese and parsley leaves and serve.