Start by bringing a large pot of salted water to a boil over high heat. Once boiling, add in the medium pasta shells and cook until just under al dente, about 6-7 minutes. Drain the pasta and set it aside.

In a large skillet, heat 1 tablespoon of olive oil over medium-high heat until shimmering. Add the ground beef and cook, stirring occasionally, until browned, about 3-5 minutes. Drain any excess fat.

In the same skillet, add additional olive oil if needed and toss in the diced sweet onion. Sauté for about 2 minutes until soft and translucent. Add minced garlic and cook for 1 minute until fragrant.

Sprinkle the all-purpose flour over the sautéed onions and garlic, whisking together and cooking for about 1 minute. Gradually whisk in the beef stock, stirring constantly. Cook until the mixture thickens, about 2-3 minutes.

Pour in the marinara sauce, followed by the Italian seasoning, dried parsley, dried oregano, and smoked paprika. Bring to a gentle boil, then reduce to a simmer. Allow it to thicken, stirring occasionally, for about 6-8 minutes.

Gently stir in the cooked pasta and browned ground beef. Mix in the heavy cream, letting it heat through for about 2-3 minutes.

Stir in the sour cream and shredded cheddar cheese until melted and everything is coated. Taste and adjust seasoning with salt and pepper as needed.

Scoop the creamy beef and shells onto plates or into bowls. Serve immediately while hot, garnishing with extra cheese or fresh herbs if desired.