Make-Ahead Breakfast Casserole

There are many version of this casserole out there but this is the one I'm expected to make for every holiday's breakfast. I've made it so often I have the recipe memorized. My mom took this same recipe and used ham instead of sausage and was met with rave results.

Make-Ahead Breakfast Casserole

6 to 8 slices of bread (original recipe says with crusts trimmed, I don't.)
2 lbs. link sausages, cooked and drained
1 Tbsp. olive oil
1 large onion, minced
8 oz. mushrooms, sliced (I usually just use two small cans of mushrooms)
5 eggs, beaten to blend
1 cup milk
1-- 10 3/4 oz. can cream of mushroom soup
1/4 tsp. ground black pepper.
1 cup shredded cheddar cheese (We usually use more than 1 cup cheese)

I had a dash or two of tabasco to the egg mix.

Butter a 9" x 13" ovenproof glass dish.
Line the bottom with bread.
Arrange cooked sausages on top.
Heat oil in skillet and saute the onions until translucent.
Add mushrooms to the skillet and saute until limp. If using canned mushrooms just heat for a few minutes.
Sprinkle onion mix on top of sausages.
Whisk eggs, milk, soup and pepper (plus tabasco if using)
Pour over onion mixture.
Top with shredded cheese.
Cover and refrigerate over night. (I sometimes make this without refrigerating and it turns out basically the same as if I had.)

Preheat oven to 350 degrees.
Bake casserole, uncovered until heated through about 40 minutes.
Serve.

If I've refrigerated the night before, I place the casserole dish in a cold oven and then preheat.