For the polenta: Heat the butter in a large Dutch oven over medium-high heat. Add the oregano, garlic and onions. Cook until softened and fragrant, about 5 minutes. Pour in the chicken stock along with 1 cup of water and bring to a boil.
Slowly add the cornmeal while whisking constantly to avoid clumping. Cook, stirring frequently, until thickened, about 20 minutes. Stir in the cream, ricotta and Parmesan. Season with salt and pepper. Cover and set aside off the heat.
For the meatballs: Add the beef and pork to a large mixing bowl. Add the breadcrumbs, milk, parsley, eggs, 3/4 cup of the Parmesan, half the garlic, 1/2 teaspoon salt and some pepper. Using clean hands, mix together until well combined. Use a scoop or your hands to form 20 evenly sized meatballs. Set them aside on a plate or baking sheet.
Add the tomatoes, olive oil, basil, oregano and remaining garlic to a 9-by-13-inch baking dish and give everything a quick stir. Transfer the meatballs to the baking dish and bake until browned, about 15 minutes. Transfer the meatballs and any pan juices to a large bowl.
For the casserole: Transfer the reserved polenta to the baking dish you just used to bake the meatballs. Place the meatballs on top of the polenta, reserving any liquid or tomatoes in the bowl. Sprinkle the remaining 3/4 cup Parmesan over the top of the casserole and bake until bubbly and golden brown, about 40 minutes.
When you are just about ready to serve, pour the pan juices into a saucepan and warm over medium heat.
Sprinkle the casserole with more grated Parmesan and chopped parsley. Serve with the warmed pan sauce on the side.
Freezer directions: Once the casserole is assembled, do not bake it. Allow the casserole to cool completely and allow the reserved sauce and tomatoes from cooking the meatballs to do the same in a separate container. This will take 45 minutes to 1 hour.
Wrap the casserole in plastic wrap and then foil. Put the sauce in a separate freezer-safe container. Label, date and freeze both until ready to eat.
To cook, allow both the casserole and sauce to thaw completely in the refrigerator, preferably overnight.
Preheat the oven to 425 degrees F. Bake the unwrapped casserole until bubbly and golden brown, about 40 minutes. Reheat the sauce in a saucepan over medium heat until heated through.