Cut loaf into 1/2-inch slices. Place 4 slices in the bottom of a sprayed 9-inch square baking pan. Spread 1 tablespoon of mustard over the bread slices. Top with ham and cheese. Spread 4 more slices of bread with the remaining tablespoon of mustard and place over cheese, mustard side down. Combine eggs and milk and pour evenly over bread.
Cover pan and refrigerate 8 hours or overnight. Remove from refrigerator and uncover. Sprinkle with corn flake crumbs and drizzle with butter. Bake on the middle shelf at 350°F for 90 minutes.