Holiday Ham and Egg Casserole

Collect all necessary components for preparation.\nSpray a 9x13-inch casserole dish with non-stick cooking spray to prevent food residue.\nPlace diced ham at the bottom of the prepared casserole dish, covering the entire surface.\nButter one side of each bread slice before cutting them into small cubes for even distribution.\nArrange the buttered bread cubes on top of the ham layer, followed by a layer of American cheese.\nIn a separate container, whisk together milk, eggs, mustard powder, and salt until well combined.\nPour the milk-egg mixture over the American cheese layer in the casserole dish, ensuring an even coating.\nCover the dish with aluminum foil and refrigerate for 8 hours or overnight to allow flavors to meld.\nPreheat your oven to 350 degrees F (175 degrees C), as specified in the original recipe.\nRemove the aluminum foil from the casserole dish before placing it in the preheated oven.\nBake the casserole in the preheated oven until the cheese is melted and the eggs are set in the middle, taking approximately 1 hour.