Sophisticated stuffing strata

Ingredients

• 12 to 15 slices white bread
• 3 small white onions , sliced
• 3 cups finely chopped celery
• 1 tbsp vegetable oil
• 2 cups sliced mushrooms
• 1/4 cup dry sherry
• 1 tbsp butter
• 2 tsp crumbled dried sage leaves
• 1 1/2 tsp dried savory
• 1/2 tsp black pepper
• 6 slices green onions
• 4 cups shredded Swiss , or blend of white cheese
• 3 1/2 cups 3.25% milk
• 7 eggs
• 1/2 tsp salt