1. Prepare Oven, Pans, and Cook Pasta:

• Preheat your oven to 350°F (175°C).
• Grease two 13×9-inch baking dishes. Set aside.
• Bring a large pot of lightly salted water to a rolling boil. Add the spiral or cavatappi pasta and cook according to package directions until al dente (tender but still firm to the bite).
• Drain the cooked pasta well in a colander and set aside.

2. Make the Meat Sauce:

• While the pasta cooks, prepare the meat sauce. In a large skillet, cook the ground beef and chopped onion over medium heat.
• Cook, breaking the beef into crumbles with a spoon or spatula, until the meat is no longer pink and the onion is softened, about 6-8 minutes.
• Drain off any excess fat from the skillet thoroughly. (Optional: Season with salt and pepper to taste here).
• Stir in the 3 ½ cups of spaghetti sauce. Bring the sauce to a simmer and let it cook for a few minutes to allow flavors to meld.

3. Combine Pasta and Sauce:

• Add the cooked and drained pasta to the skillet with the meat sauce.
• Stir gently but thoroughly to ensure all the pasta is evenly coated with the sauce.

4. Assemble the Casseroles:

• Divide the pasta and meat sauce mixture evenly between the two prepared greased 13×9-inch baking dishes. Spread it into an even layer in each dish.
• Sprinkle 2 cups of the shredded mozzarella cheese over the top of the pasta mixture in each baking dish (for a total of 4 cups cheese used).
• Arrange the sliced pepperoni evenly over the cheese layer on both casseroles.

5. Bake:

• Place both baking dishes in the preheated oven.
• Bake, uncovered, for 25-30 minutes.
• The Pizza Casserole is done when it is heated through completely and the cheese topping is melted, bubbly, and perhaps lightly golden brown in spots.

6. Rest and Serve:

• Let the casseroles cool for a few minutes (5-10 minutes) before serving. This allows the layers to set slightly and makes serving easier.
• Slice into squares and serve hot. Enjoy your delicious Pizza Casserole!