Cook bacon until crisp in large pan; remove bacon and keep warm. Reserve 1/4 cup bacon drippings in pan.
Cook hash browns with 1/3 cup green onions in drippings until golden brown.
Heat oven to 375° F. In a spray-coated 10x12x2-inch steamtable pan, layer the hash browns, bacon and hard-cooked egg slices. Sprinkle on the seasonings and 2 cups of cheese.
Stir and heat melted butter, sour cream, flour and milk in a saucepan until smooth and thickened, about 2 to 3 minutes. Pour over ingredients. Sprinkle on remaining cheese and green onions.
*If using peeled, hard-cooked egg product.
Bake casserole 30 to 35 minutes until browned and bubbly and internal temperature has reached a minimum of 160° F. Cut pan 3×4. Top each piece with a half tablespoon of sour cream and 1/2 teaspoon chives. Serve immediately.