1: Heat your skillet over medium heat and cook and stir sausage until crumbly and completely browned, usually about 10 minutes. Transfer cooked sausage to the prepared casserole dish.
2: Cook and stir mushrooms in the same skillet over medium heat until liquid has been released and mushrooms are lightly browned, 5 to 10 minutes then drain excess liquid.
3: Mix mushrooms, eggs, bread, canna - milk, Cheddar cheese, ham, spinach, flour, mustard powder, salt, butter, and basil together in a large bowl pour over sausage. Cover casserole dish and refrigerate, 2 hours to overnight to allow flavors to come out.
4: In the morning preheat you oven to 350 degrees F. Bake in the preheated oven until a knife inserted into the center of the strata comes out clean usually 60 to 70 minutes depending on your oven.