In a large pot, bring salted water to a boiling point. Add medium pasta shells and cook according to the package instructions until just under al dente, about 8-10 minutes. Drain the pasta and set aside.

Heat a large skillet over medium-high heat and add a drizzle of olive oil. Once the oil shimmers, add the ground beef and sauté for about 3-5 minutes until browned. Drain excess fat.

In the same skillet, add the diced sweet onion and sauté for 2 minutes until translucent. Then add minced garlic and cook for an additional minute until fragrant.

Sprinkle all-purpose flour over the beef and aromatics in the skillet. Stir continuously for about 1 minute until lightly browned. Gradually whisk in beef stock and marinara sauce, then stir in Italian seasoning, parsley, and smoked paprika.

Bring the sauce to a boil, then reduce to a gentle simmer. Cook for about 6-8 minutes, stirring occasionally until it thickens slightly.

Stir the cooked pasta into the simmering sauce, ensuring each shell is well coated. Add in the heavy cream, sour cream, and cheddar cheese until fully melted and heated through.

Garnish with fresh parsley if desired, and serve hot.