Bring a large pot of heavily salted water to a rolling boil. Add pasta shells and cook according to package directions until al dente, usually 9-10 minutes. Drain in colander and set aside. Do not rinse.

While pasta cooks, heat a large, deep skillet over medium heat. Add ground beef and finely chopped onion. Cook together for 6-7 minutes, breaking beef into small crumbles with a wooden spoon, until beef is no longer pink and onion is soft and translucent. Add minced garlic and cook for 1 more minute, stirring constantly. Drain excess fat if more than 1 tablespoon accumulates.

Pour beef broth into the skillet, scraping bottom to release any browned bits. Stir in Italian seasoning. Bring to a gentle simmer and cook for about 5 minutes, allowing liquid to reduce slightly and flavors to concentrate.

Reduce heat to low. Pour in heavy cream, stirring to incorporate smoothly. Simmer gently for 5 minutes, stirring occasionally, until sauce thickens slightly and coats the back of a spoon. Do not allow to boil hard.

Add drained pasta shells to the skillet. Gently fold pasta into the sauce using tongs or large spoon, ensuring every shell gets coated inside and out. Toss for 1-2 minutes to allow pasta to absorb some sauce. Taste and adjust seasoning with salt and black pepper as needed.

Transfer to serving bowls or plates while hot. Garnish with a light sprinkle of Italian seasoning if desired. Serve immediately.