Begin by filling a large pot with water, adding a pinch of salt, and bringing it to a rolling boil over high heat. Add the medium pasta shells and cook according to the package instructions until just under al dente, about 7-8 minutes. Drain the shells and set them aside.

In a large skillet, heat 2 tablespoons of olive oil over medium-high heat until shimmering. Add 1 pound of ground beef, breaking it apart with a spatula, and cook for about 3-5 minutes or until browned. Drain any excess fat from the skillet.

To the skillet with the beef, add one diced sweet onion and sauté for about 2 minutes until the onion becomes translucent. Next, add 2 cloves of minced garlic and continue sautéing for another minute, or until fragrant.

Sprinkle 2 tablespoons of all-purpose flour over the beef and onions, stirring constantly for about 1 minute to form a roux. Gradually whisk in 2 cups of beef stock and 1 cup of marinara sauce, then blend in 1 teaspoon each of Italian seasoning, dried parsley, and smoked paprika.

Bring the sauce to a gentle boil, then reduce the heat to low and let it simmer for 6-8 minutes, stirring often.

Stir the drained pasta shells and browned beef back into the skillet, ensuring they're well coated in the creamy sauce. Pour in ½ cup of heavy cream and ¼ cup of sour cream, stirring to combine thoroughly until heated through.

Finally, sprinkle 1 cup of shredded cheddar cheese over the mixture, folding it in gently until completely melted and creamy. Serve immediately and enjoy this warm bowl of comfort!