Butter a 9x13 inch baking dish generously, or spray it with cooking oil.
Cut and fit 5-6 slices of bread (crusts removed!) to fill the entire bottom of dish.
Add half the shredded cheddar cheese and all of the diced peppers on top of the first layer of bread. Cut and fit the remaining 5-6 slices of bread to completely cover the peppers and cheese. Then, add the other half of cheese on top.
In a large bowl, whisk together your eggs with the pepper, mustard powder, onion powder, chives, Worcestershire sauce (if using), and hot sauce. Add the milk and whisk until well combined. Pour the egg mixture evenly over the casserole.
Cover your casserole dish with tin foil and pop it into the fridge to rest overnight (or for AT LEAST an hour)
In the morning, remove the casserole from the fridge and take off the tin foil. Then, preheat your oven to 350F.Melt your butter, and combine it in a bowl with the Cornflakes. Add this mixture evenly over the top of the casserole. Bake the casserole in your preheated oven (on the middle rack) until the casserole is set and lightly browned — about 60-70 minutes. Let casserole stand for 10 minutes before cutting and serving.