Place 8 slices of cubed bread on the bottom a 9 x 13 inch baking dish. Top with ham and cheeses and then the remaining cubed bread.
In a large bowl, whisk together eggs, milk, garlic powder, ground mustard, and peppers. Pour over bread, ham, and cheese. Cover and refrigerate 8 hours (or overnight).
Remove from fridge 30 minutes before cooking.
Preheat oven to 375 degrees.
In a small bowl, mix together crushed cornflakes and melted butter. Sprinkle over top the casserole and bake for 40-45 minutes, until a knife inserted in the center comes out clean.
Serve warm.
Notes
If you have bread that is getting a little stale and at the end of whether or not you would use it in a sandwich, that is good bread for this casserole. But a new loaf will work too.