Bring a large pot of salted water to a boil. Cook the pasta shells according to package directions until al dente. Reserve 1/4 cup of the pasta water, drain, and set the shells aside.

In a large skillet, heat the olive oil over medium-high heat. Add the sausage bites and cook until browned and fully cooked, about 5–6 minutes. Remove from the skillet and set aside.

Lower the heat to medium and add the butter and minced garlic to the skillet, cooking for about 30 seconds, or until fragrant.

Pour in the heavy cream and chicken broth, bringing the mixture to a gentle simmer. Stir in the grated Parmesan cheese (and mozzarella if desired) until the sauce is creamy and smooth.

Toss in the cooked pasta shells, coating them well with the sauce. If the sauce seems too thick, gradually add some of the reserved pasta water to achieve the desired consistency.

Return the sausage bites to the skillet, mixing everything together and allowing it to simmer for an additional 1–2 minutes so the flavors meld.

Finally, sprinkle with Italian seasoning, adjust seasoning with salt and black pepper to taste, and garnish with chopped parsley or basil before serving hot.