1. Soak the sweetbreads in ice water forty-five minutes. Meanwhile, bring to a boil enough water to cover the sweetbreads, and add the vinegar and one teaspoon salt. Drop the sweetbreads into the boiling liquid and simmer until white, fifteen to twenty minutes. Drain, cool in ice water and remove all covering and connective tissues. Preheat broiler.
2. Split the sweetbreads and season with salt and pepper. Roll in the melted butter, then in the crumbs. Sprinkle with more butter and broil about five inches from the source of heat until well browned. Broil the ham and mushrooms brushed with butter at the same time, or saute the mushrooms in butter.
3. Place a slice of ham on each slice of toast, add the sweetbreads and top with a mushroom. Lightly brown remaining butter and pour over the top.