Place the broccoli in a steamer basket; place in a large saucepan over 1 in. of water. Bring to a boil, cover and steam for 5-7 minutes or until crisp-tender. Meanwhile, in a large skillet, saute the mushrooms in the butter until tender.
In a greased 13x9x2 in. baking dish, layer 4 cups chicken, two-thirds of the mushrooms, two cans of water chestnuts and 4 cups broccoli. In a greased 8 in. square baking dish. layer the remaining chicken, mushrooms, water chestnuts and broccoli.
In a large saucepan over medium heat, melt butter. Stir in flour, seasoned salt and pepper until smooth. Gradually add the broth and whipping cream. Bring to a boil; cook and stir for 2 minutes or until thickened and bubbly. Remove from the heat.
Stir in a small amount of the hot mixture to egg yolks. Return all to pan, cook and stir until mixture reaches 160 degrees and coats the back of a metal spoon. Remove from heat, stir in lemon juice and nutmeg.
Pour 3 cups of sauce over the large casserole and remaining sauce over the small casserole; sprinkle with almonds. Bake, uncovered, at 375 degrees for 20-25 minutes or until bubbly and heated through.