Bring a large pot of salted water to a boil and add medium pasta shells. Cook according to package instructions until just under al dente, usually 8-10 minutes. Drain the shells and set them aside.

In a large skillet, heat a tablespoon of olive oil over medium-high heat. Add the ground beef, breaking it apart with a spatula. Cook for 3-5 minutes until browned, then drain excess fat.

In the same skillet, lower the heat slightly and add diced sweet onion. Sauté for about 2 minutes until translucent. Add minced garlic and continue for another minute until aromatic.

Sprinkle all-purpose flour over the beef mixture, stirring to incorporate. Gradually whisk in beef stock and then add marinara sauce, Italian seasoning, dried parsley, dried oregano, and smoked paprika.

Increase the heat until the mixture reaches a gentle boil, then reduce to low and let it simmer for 6-8 minutes, stirring occasionally.

Stir in the cooked pasta shells and browned beef. Pour in the heavy cream and stir gently for 1-2 minutes. Taste and season with salt and pepper.

Remove from heat and fold in the sour cream and cheddar cheese until melted. Garnish with chopped parsley if desired.

Dish out the creamy beef mixture onto plates and serve immediately.