HEAT oven to 400°F.
BEAT eggs and sour cream with whisk until well blended. Pour into greased 13x9-inch baking dish. Bake 10 min. or until egg mixture is softly set. Meanwhile, cook sausage, mushrooms and onions in large skillet on medium heat 6 to 8 min. or until sausage is cooked through, stirring occasionally. Drain.
REDUCE oven temperature to 325°F. Spoon tomatoes over the baked egg layer; top with sausage mixture. Sprinkle with cheeses.
BAKE 30 min. or until egg mixture is set in center.
Here are my other favorite brunch casseroles: Good Morning Grits and Sausage Casserole
I hope everyone has a wonderful holiday weekend!!
(photo and recipe from kraftfoods.com)