In a large skillet, cook beef over medium heat until no longer pink;
drain. Place half in a greased 2-qt. baking dish. Layer with
mushrooms, two-thirds of the onions and all of the vegetables. Top
with remaining beef
In a saucepan, combine soup and 1/2 cup sour cream; cook over
low heat until heated through. Pour over beef. Cut each biscuit in
half; arrange cut side down around edge of dish. Sprinkle remaining
onions in center of casserole. Combine egg, celery seed, salt and
remaining sour cream; drizzle over biscuits. Bake, uncovered, at
375 degrees F for 25-30 minutes or until golden brown