Step 1

Cook sausage and onion, drain, crumble and set aside.  In a large bowl, beat eggs and add milk, cheese, salt and pepper, dry mustard and sausage/onion mixture.

Step 2

Spray a 9x13 baking dish with olive oil spray and place bread cubes in the bottom of the pan (make sure that cubes are in small pieces.)

Step 3

Pour egg mixture on top.  Cover and refrigerate overnight.

Step 4

The next morning, preheat the oven to 350 degrees.  Bake casserole, uncovered, for 1 hour.