Heat oven to 350°F. Prepare a baking dish by liberally greasing with 1 ounce of butter. Set aside.
In a medium non-stick sauté pan, gently sauté apples, onion, and celery in 2 ounces of the butter until soft. Add cider, nutmeg, salt and pepper. NOTE: you may either peel your apples or leave the skin on. I use two apples, peeling one and leaving the skin on the other.
Simmer on very low heat, covered, for 1/2 hour until the vegetables are very soft.
Melt the remaining 1 ounce of butter and add the flour to the melted butter. Whisk until the flour is incorporated.
To the pan of vegetables, add the flour mixture and the cream and bring to a boil. Allow to cook over high heat for 2 minutes. The mixture will thicken. Remove from the heat. Add chicken and stir.
In a medium bowl, combine the breadcrumbs with 2 ounces of melted butter. Stir to combine. NOTE: if using homemade bread crumbs, consider adding dried herbs to enhance their flavor such as oregano, basil, and marjoram.
Pour the chicken mixture into the prepared baking dish and sprinkle with the breadcrumbs.
Bake for 20 minutes or until casserole bubbles. Serve over Spätzle, wide noodles, or rice.