This is a recipe from my "Taste of Home Contest Winners" magazine. I modified it a bit to suit our tastes. I prefer to grill the chicken(adds even more flavor), that I had brushed with olive oil and seasoned, and then cut it up and add to the ricotta mixture. This recipe serves 10, so I freeze 3/4 of the shells to make in the future.
Meanwhile, in a large skillet, brown chicken in 1 tablespoon oil (or brush chicken with olive oil and season, then grill chicken and then cut into pieces). Remove and set aside. In the same pan, saute mushrooms in remaining oil until tender; set aside. In a small bowl, combine the egg, ricotta, 1 cup Parmesan, mozzarella and seasonings.
Drain and rinse pasta with cold water; stuff each shell with about 1 tablespoon of cheese mixture. Place in a greased 13x9-in. baking dish. Top with chicken and mushrooms.
In a large saucepan over medium heat, melt butter. Add garlic; cook and stir for 1 minute. Add cream; cook 5 minutes longer. Add 1 cup Parmesan cheese; cook and stir until thickened.
Pour sauce over the casserole. Sprinkle with remaining 1/2 cup Parmesan cheese. Cover and bake at 350° for 30 minutes. Uncover; bake 10-15 minutes longer or until bubbly.
If desired, cover and freeze unbaked shells for up to 1 month. If freezing, may want to cut back on the amount of sauce you make for the current meal. Then make fresh sauce when you use the frozen shells.
To use frozen shells: Thaw in the refrigerator. Let stand at room temperature for 30 minutes. Bake as directed. Yield: 10 servings.