Trim crusts from bread; reserve crusts. Cover bottom of greased 13 x 9-inch (33 x 23 cm) baking dish with slices of bread, trimming to fit if necessary. Cover with ham, then cheese. Top with another layer of bread.
Whisk eggs. Add onion, green pepper, dry mustard, pepper, Worcestershire sauce and Tabasco; whisk to combine. Whisk in milk. Pour mixture over bread. Cover and refrigerate overnight.
Meanwhile, pulse reserved crusts in food processor until coarsely chopped. Set aside 1-1/2 cups of the bread crumbs. (Remainder can be frozen for another use.)
The next day, stir butter into bread crumbs until moistened. Sprinkle buttered crumbs over top of casserole.
Bake in a preheated 350 degrees F (180 degrees F) oven until puffed, set and golden brown, about 1 to 1-1/4 hours.