01 - Preheat oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
02 - Bring a large pot of salted water to a boil. Cook pasta shells al dente according to package instructions. Drain and set aside to cool slightly.
03 - In a medium saucepan over medium heat, melt butter. Add minced garlic and sauté 1 minute until fragrant. Stir in heavy cream and bring to a gentle simmer. Reduce heat to low, whisk in Parmesan, nutmeg, salt, and pepper. Cook, stirring occasionally, until slightly thickened for 4–5 minutes. Remove from heat.
04 - In a large bowl, combine shredded chicken, ricotta, 1/2 cup mozzarella, 1/4 cup Parmesan, egg, parsley, garlic powder, salt, and pepper. Mix until well blended.
05 - Spread 1 cup of Alfredo sauce over the bottom of the prepared baking dish.
06 - Fill each cooked shell with approximately 2 tablespoons of chicken filling and arrange stuffed shells in a single layer in the dish.
07 - Pour the remaining Alfredo sauce evenly over the shells. Sprinkle with the remaining mozzarella and Parmesan cheese.
08 - Cover the dish with aluminum foil and bake for 20 minutes. Remove foil and bake for an additional 10–15 minutes, until the cheese is melted and bubbly.
09 - Let the dish rest for 5 minutes before serving. Garnish with fresh parsley if desired.