1 can semi-condensed cream of mushroom soup or cream of chicken soup
1/4 c. mayonnaise
1/4 c. sour cream
1 egg yolk
1 (10 oz.) pkg. frozen chopped broccoli, thawed and drained
1 (10 oz.) pkg. frozen whole kernel corn, thawed and drained
1 c. shredded Swiss cheese
1/2 c. finely chopped onion
1/3 c. Swiss cheese flavored snack cracker crumbs
1 tbsp. butter, melted

Preheat oven to 350 degrees. Mix the first 4 ingredients. Stir in the broccoli, corn, cheese and onion. Spoon into ungreased shallow 1 1/2-quart baking dish. Stir together the crumbs and butter. Sprinkle over the casserole. Bake 30-35 minutes.