-In a large casserole dish (I make life easier by using a disposable aluminum pan), sprayed with cooking spray, layer the bread evenly on the bottom of the pan.
-Top the bread layer evenly with the ham.
-In a large bowl, whisk together the eggs, milk, salt, pepper, and dry mustard.
-Pour the egg mixture evenly over the bread and ham in the casserole dish.
-Top with the shredded cheeses.
-Top the cheeses with the cornflake crumbs and then drizzle the butter over the top of the corn flakes.
-Cover the entire dish with parchment paper and then aluminum foil and allow the casserole to sit in the fridge at least overnight or for up to 2 days.
-Allow the casserole to sit on the counter for about an hour before you're ready to bake it.
-Preheat the oven to 375 degrees Fahrenheit (190 degrees Celsius)
-Place the covered casserole in the oven and bake for 1 hour.
-Uncover and continue baking for about 15-20 minutes.
-Allow the casserole to sit for about 10 minutes before serving.
Notes
Cover and refrigerate any leftovers for up to 5 days.Reheat (covered) in an oven or air fryer until hot.