Stir in the minced garlic and cook for 30 seconds, just until fragrant, being careful not to let it brown.
Add the ground beef, salt, and black pepper to the Dutch oven. Cook, breaking the meat up with a wooden spoon, for 5 to 7 minutes, until the beef is fully browned and no pink remains. If there is excess grease, carefully spoon off most of it, leaving just a thin layer for flavor.
Turn off the heat under the Dutch oven for a moment. Pour the uncooked pasta shells directly over the browned beef and gently spread them into an even layer. Do not stir yet; you want the shells mostly on top of the meat so the creamy liquid can soak through them.
In a large measuring cup or mixing bowl, whisk together the beef broth, heavy cream, tomato paste, and Italian seasoning until the tomato paste is fully dissolved and the mixture is smooth and uniform. Whisk in 1 cup of the shredded cheddar cheese until it starts to melt into the liquid. If using, whisk in the crushed red pepper flakes. This is your one creamy liquid mixture.
Return the Dutch oven to medium heat. Slowly pour the creamy liquid mixture evenly over the uncooked pasta shells and browned beef in the Dutch oven, making sure to cover as much of the pasta as possible. Use the back of a spoon to gently press any exposed shells down into the liquid so they can cook evenly, but avoid heavy stirring.
Bring the mixture just up to a gentle simmer, then reduce the heat to low. Cover the Dutch oven with a lid and cook for 15 to 18 minutes, stirring once or twice during cooking to prevent sticking, until the pasta shells are tender and most of the liquid has thickened into a creamy sauce.
Remove the lid and check the consistency. If the sauce seems too thick, stir in a splash of beef broth or water, a tablespoon at a time, until it looks creamy and loose enough to coat the shells. If it’s too thin, let it simmer uncovered for 2 to 3 more minutes, stirring frequently, until slightly reduced.
Turn off the heat. Stir in the remaining 1/2 cup shredded cheddar cheese until melted and the sauce is velvety. Taste and adjust seasoning with additional salt and black pepper if needed.
Let the creamy beef and shells rest for 3 to 5 minutes with the lid slightly ajar; this helps the sauce cling to the pasta and makes the dish feel extra hearty. Sprinkle with grated Parmesan and chopped fresh parsley, if using, and serve hot straight from the Dutch oven.
To lighten this dish up a bit, you can use half-and-half in place of some of the heavy cream (try 1 cup heavy cream and 1/2 cup half-and-half) and choose a leaner ground beef. For extra veggies without extra pans, stir in 1 to 2 cups of frozen peas or mixed vegetables during the last 5 minutes of simmering, or sauté diced bell peppers with the onion at the beginning. If you prefer a different cheese profile, swap some or all of the cheddar for mozzarella, Colby Jack, or a smoky cheddar. For a bit more Italian flair, add 1/4 teaspoon fennel seeds and a pinch of red pepper flakes to the beef as it browns, or stir in a handful of baby spinach at the end until wilted. You can also make this ahead for meal prep: cook as directed, let it cool, then portion into containers. When reheating, add a splash of broth or milk to bring the sauce back to a creamy texture. If you’re cooking for kids, keep the seasoning mild and serve red pepper flakes on the side so everyone can adjust the heat at the table.
