In a large skillet, heat the olive oil over medium heat. Add the diced onion and cook until translucent, about 3-4 minutes. Stir in the minced garlic and cook for an additional 1 minute until fragrant.
Add the ground beef to the skillet, breaking it apart with a spatula. Cook until browned and no longer pink, about 5-7 minutes. Drain any excess fat.
Stir in the diced tomatoes (with juices), beef broth, Italian seasoning, salt, and black pepper. Bring the mixture to a simmer.
Add the shell pasta to the skillet, stirring to combine. Cover and cook for about 10-12 minutes, or until the pasta is al dente, stirring occasionally.
Reduce the heat to low and stir in the heavy cream and shredded cheddar cheese. Cook until the cheese is melted and the sauce is creamy, about 2-3 minutes.
Remove from heat and garnish with chopped parsley before serving.