Preheat oven to 375°. Pulse 1 slice bread in a food processor to make coarse crumbs. Mix with beef, parsley, salt, black pepper, and egg whites. Shape mixture into 4 (1 1/2-inch-thick) loaves. Place on a lightly oiled baking sheet, and bake at 375° for 30 minutes, or until done. Place potatoes in a vegetable steamer; top with corn. Steam, covered, 25 minutes, or until tender. Transfer to a large bowl; add butter, and mash with a potato masher.