Begin by boiling a generously salted pot of water. Add the pasta shells and cook according to the instructions on the packaging until al dente. Once done, drain thoroughly and reserve.

In a broad skillet set over medium heat, sauté the ground beef along with the diced onion and red bell pepper until the meat is browned and crumbled. Remove excess grease, then return the pan to the stovetop.

Incorporate the minced garlic, Italian seasoning, salt, and pepper, stirring until the mixture releases its aroma. Add the butter and mix until fully melted. Sprinkle in the flour, stirring constantly for about one minute to ensure it integrates smoothly.

Pour in the beef broth slowly, whisking continuously until the sauce reaches a slightly thickened consistency. Blend in the sour cream and shredded cheddar cheese, stirring until fully melted and cohesive.

Reintroduce the cooked pasta shells, folding them gently into the sauce. Garnish with chopped parsley before serving.