Bring a large pot of salted water to a rolling boil over high heat. Add the medium pasta shells and cook according to package instructions until al dente, usually about 8-10 minutes. Once cooked, drain the shells thoroughly and set them aside.

In a large cast iron skillet, heat 2 tablespoons of olive oil over medium-high heat. Add the ground beef to the skillet and cook for about 3-5 minutes until browned. Drain excess fat and transfer the beef to a plate, keeping the skillet on the heat.

In the same skillet, add the diced sweet onion and sauté over medium heat for about 2-3 minutes until translucent. Then, add the minced garlic and Italian seasoning, cooking for an additional minute until fragrant.

Sprinkle in 2 tablespoons of all-purpose flour to the sautéed onions and garlic, stirring constantly for about 1 minute until the flour turns a light golden brown.

Gradually whisk in 2 cups of beef stock and 1 cup of tomato sauce, bringing to a gentle boil. Once boiling, reduce the heat and simmer for 6-8 minutes until slightly thickened.

Stir in the cooked pasta shells, reserved ground beef, and 1 cup of heavy cream. Heat through for 1-2 minutes until pasta is coated.

Remove from heat and stir in 1 cup of shredded extra-sharp cheddar cheese. Allow to melt into the sauce for about 2 minutes. Season with kosher salt and black pepper to taste.