Hot Chicken Sandwich Casserole

4 large chicken breasts, cooked and diced
3 boiled eggs, chopped
1 small jar mushrooms
1/2 cup mayonnaise
1 small onion, diced
16 slices thin white bread
1 can cream of chicken soup
1 (8 ounce) container sour cream

Butter bread on both sides and cut off crusts. Place 8 slices in rectangular baking dish, side by side. Mix together remaining ingredients and spread over bread slices. Top with other 8 slices of bread.

Mix together cream of chicken soup and sour cream. Spread over top layer of bread. Refrigerate overnight.

Bake in preheated oven at 300 degrees F for 1 hour.

Set oven to 350 degrees F for 5 minutes to brown top lightly.

Cut into squares to serve.