1. Preheat oven to 400 degrees. Lightly grease a 3-quart rectangular baking dish; set aside.
2. In a large saucepan, bring broth and butter to boiling. Meanwhile, in a medium bowl, stir together milk and cornmeal. Slowly add cornmeal mixture to boiling broth, stirring constantly. Cook and stir until mixture returns to boiling. Reduce heat to low. Cook for 10 minutes or until mixture is very thick, stirring frequently. Remove from heat. Stir in ricotta cheese cheese, 1/2 cup of the mozzarella cheese, and 1/4 cup of the Asiagopolenta in the prepared baking dish; set aside.
3. In a very large skillet, cook sausage, mushrooms, onion, and garlic over medium heat until meat is brown and onion is tender. Drain off fat. Stir in pasta sauce; heat through. Spoon sausage mixture over polenta in dish, spreading evenly. Dollop remaining polenta on top of sauce and sprinkle with the remaining mozzarella and Asiago cheeses.
4. Bake, uncovered, for 30 minutes or until top is lightly golden and set. Let stand for 10 minutes before serving. Garnish with fresh basil. Makes 8 servings.
*Note: If using the quick-cooking polenta mix, once the polenta mixture returns to boiling in Step 2, cook and stir for only 3 to 5 minutes or until mixture is very thick.