Start by bringing a large pot of salted water to a boil. Add your pasta shells and cook according to package instructions until al dente. Reserve 1 cup of the pasta water, then drain the rest and set the pasta aside.
In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté for about 3-4 minutes until it becomes translucent. Add the minced garlic and crushed red pepper, cooking for an additional minute until fragrant.
Increase the heat to medium-high and add the ground beef to the skillet. Break it apart with your spoon, seasoning with salt and cracked pepper. Cook until the beef is browned and cooked through, about 5-7 minutes. Drain excess fat if necessary.
Stir in the diced tomatoes (with their juices), tomato paste, beef broth, and Italian seasoning. Bring the mixture to a gentle simmer, allowing it to cook for about 5 minutes to meld the flavors.
Add the baby spinach to the skillet and stir until it wilts, about 2 minutes. Next, pour in the heavy cream, stirring to combine. If the sauce is too thick, gradually add some reserved pasta water until you reach your desired consistency.
Fold in the cooked pasta shells and Parmesan cheese, mixing until everything is well-coated in the creamy sauce. Taste and adjust seasoning if necessary.
Remove from heat and serve immediately. You can top with additional Parmesan cheese and a sprinkle of fresh herbs if desired.
