From Carol Gordon't Sleep On It
5 cups cubed day-old bread
3 T butter, melted
2 T olive oil
1 pound mushrooms
1/2 c. diced celery
1/2 cup diced peppers
1/2 cup diced onions
1/2 cup mayonnaise
Salt and freshly groung pepper
1/2 c milk
2 large eggs
1 cup condensed cream of mushroom soup
Place the bread in a large bowl and drizzle with the melted butter; toss to combine. Spread about 2 cups of the bread across the bottom of a 9x13 inch glass baking pan. Place a large skillet over medium heat and add the olive oil and mushrooms, sauteeing until tender. Remove from the heat and add the celery, onions, peppers, and mayonnaise. Season to taste with salt and pepper and then spread this over the bread
Top with 2 cups of bread cubes. In a small bowl, beat together the milk and eggs until blended and poour over the casserole. Cover and refrigerate overnight.
Preheat the Over to 325. Pour the cream of mushroom soup over the casserole and top with remaining cup of bread cubes. Bake, uncovered, until browned, about one hour.
