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