• Preheat the oven to 375 degrees Fahrenheit. Spray a 3-quart baking dish with nonstick cooking spray and set aside.
• Bring a large pot of salted water to a rolling boil, then cook 1 (12-ounce) box jumbo shell pasta according to the directions on the package for al dente pasta. If preferred, undercook by a few minutes to avoid overcooking in the oven. 
• Drain the shells and rinse them with cold water to stop the cooking process. Toss lightly with 1-2 teaspoons of olive oil or vegetable oil to prevent them from sticking.

Filling

• Add 1 ½ cups cooked, chopped chicken, 1 cup whole-milk ricotta cheese, 1 ½ cups shredded mozzarella, ½ cup grated parmesan, ⅓ cup chopped sun-dried tomatoes, ½ teaspoon Italian seasoning, ¼ teaspoon salt, and ¼ teaspoon ground black pepper to a large bowl and mix until combined. Set aside.

Sauce

• Add 3 tablespoons unsalted butter to a large skillet and melt over medium heat. Once melted, add 2 teaspoons minced garlic and cook for about 30-60 seconds, until fragrant. Add 3 tablespoons all-purpose flour and stir to form a paste.
• Cook for 1-2 minutes before slowly whisking in 2 cups chicken broth, 1 cup heavy whipping cream, and 1 cup grated parmesan cheese until smooth and combined. It will be quite thick as you first begin to whisk in the liquid.
• Stir in 1 cup chopped sun-dried tomatoes, 1 teaspoon paprika, 2 teaspoons Italian seasoning, salt, and ground black pepper. Continue to whisk the sauce for a few minutes until it thickens.

Assembly

• Add about ¾ of the sauce to the bottom of the prepared baking dish.
• Stuff each shell with about 2 tablespoons of the filling, then arrange the filled shells in an even layer on top of the sauce.
• Spoon the remaining sauce evenly over the top of the shells.
• Bake uncovered for 25-30 minutes, until the sauce is bubbling and the shells are starting to brown. Let the dish rest for about 5 minutes before garnishing with fresh basil if desired, and serving.