Bring a large pot of salted water to a boil. Add medium pasta shells and cook according to package instructions, about 8-10 minutes until al dente. Drain and set aside.

In a large skillet over medium-high heat, heat 1 tablespoon of olive oil. Add 1 pound of ground beef and cook for 5-7 minutes until browned. Drain excess fat and set aside.

In the same skillet, add another tablespoon of olive oil if needed, and reduce heat to medium. Sauté finely chopped sweet onion for about 2 minutes until translucent. Add minced garlic and cook for an additional minute.

Sprinkle in 2 tablespoons of all-purpose flour over the onion and garlic mixture, whisking continuously for about a minute until lightly golden.

Gradually pour in 2 cups of beef stock and 1 cup of marinara sauce. Add dried Italian seasoning, parsley, oregano, and smoked paprika. Bring to a boil, then reduce heat and simmer for 6-8 minutes.

Stir in the reserved cooked pasta and browned beef. Add 1 cup of heavy cream, and season with salt and pepper to taste. Heat through for 2-3 minutes.

Remove from heat and stir in ½ cup of sour cream and 1 cup of cheddar cheese until melted. Serve immediately.

Garnish with chopped parsley for freshness before serving.