Cook the pasta: In a large pot of boiling salted water, cook 8 oz medium pasta shells according to package instructions until al dente. Drain well and set aside.
Brown the beef: In a large skillet, heat 1 tbsp olive oil over medium-high heat. Add 1 lb ground beef and cook until browned, about 3-5 minutes. Drain excess fat if necessary.
Sauté the onion and garlic: In the same skillet, add 1 small diced sweet onion and sauté until translucent, about 2 minutes. Add in 5 minced cloves of garlic and sauté for another minute until fragrant.
Incorporate flour: Whisk in 2 tbsp all-purpose flour and cook for 1 minute until lightly browned.
Add liquids and seasonings: Gradually add 1 cup beef stock, 1 (15 oz) can of marinara sauce, 1 tsp Italian seasoning, 1 tsp dried parsley, 1/2 tsp dried oregano, and 1/2 tsp smoked paprika. Bring to a boil and then reduce heat to simmer until the sauce thickens, about 6-8 minutes.
Combine pasta and beef: Add the cooked pasta and browned beef back into the skillet, stirring to combine.
Make it creamy: Stir in 3/4 cup heavy cream until heated through, then mix in 1/4 cup sour cream.
Cheesy finish: Fold in 1 1/2 cups freshly grated cheddar cheese until melted, approximately 1-2 minutes. The sauce should be creamy and smooth.
Serve: Serve immediately, garnished with additional parsley if desired.