Preheat your oven to 350°F. This is an important step to ensure even cooking. While the oven heats up, spray a 9×13-inch baking dish with nonstick spray and set it aside.
In a large skillet set over medium-high heat, add the ground beef. Brown it until it’s no longer pink, about 5 to 7 minutes. Use a slotted spoon to transfer the cooked beef to a paper towel-lined bowl. This helps drain the excess fat, keeping your casserole from getting greasy.
Add the diced onion and diced bell pepper to the skillet, sautéing in the leftover fat for 2 to 3 minutes. The vegetables should soften slightly. Then, add the minced garlic and cook for an additional 30 seconds until fragrant.
Return the browned beef to the skillet. Stir in the diced tomatoes, tomato paste, kosher salt, Italian seasoning, ground black pepper, and Worcestershire sauce. Bring the mixture to a boil, then reduce the heat and let it simmer for 5 minutes. This allows the flavors to meld beautifully.
While the beef mixture is simmering, bring a pot of water to a boil and add the dry shell pasta. Cook according to package instructions, then drain and transfer it to a large bowl.
To the drained pasta, add the cream cheese, sour cream, and melted butter. Mix well until the pasta is coated in that creamy goodness. You want to ensure every noodle gets covered!
Spread half of the creamy pasta mixture in the bottom of your prepared baking dish. Top with half of the beef mixture, making sure to distribute it evenly. Repeat with the remaining pasta and beef layers, finishing with a layer of shredded cheddar cheese and mozzarella cheese.
Place the casserole in the oven and bake uncovered for 25 to 30 minutes, or until the dish is heated through. If you want a bubbly, golden top, you can broil it for an additional 1 to 2 minutes.
Once done, remove the casserole from the oven and let it rest for 10 minutes before serving. This resting time allows the layers to set, making it easier to serve.
