Broccoli Puff

1/2 cup chopped onion
1 tablespoon butter or margarine
1 (10-ounce) package frozen chopped broccoli, thawed and well-drained
2 cups cooked rice
1 (10 3/4-ounce) can condensed cream of mushroom soup
1/4 teaspoon ground thyme
1 teaspoon Worcestershire sauce
4 large eggs, separated
2 cups (8 ounces) shredded Cheddar cheese

1. Cook onion in butter in small skillet until tender. Combine onion with broccoli, rice, soup, thyme and Worcestershire sauce in greased shallow 2-quart baking dish. Bake at 400 degrees 20 minutes.
2. Meanwhile, beat egg yolks until thick and lemon-colored; add cheese. Beat egg whites until soft peaks form; fold in egg yolk mixture. Remove baking dish from oven; stir. Spread egg mixture over top. Bake 10 to 15 minutes or until golden brown.