Overnight Breakfast Casserole

INGREDIENTS

For the casserole:

1 lb

ground breakfast sausage

4 cups

sharp cheddar cheese, grated

eggs

large onion, chopped

red bell pepper, chopped

1 cup

heavy whipping cream

1/4 cup

green onion, chopped (1/2 cup?)

8 oz

sliced mushrooms

Kosher salt and freshly ground pepper,

For the gravy:

2 cups

milk

1/4 cup

all-purpose flour

1 tbsp

butter or oil

Kosher salt and freshly ground pepper,