In a large saucepan, place sweetbreads, 1/4 cup white vinegar, 1 teaspoon salt and cold water to cover and bring to boil. Remove from heat and allow to stand 10 minutes. Remove sweetbreads and cool in refrigerator 30 minutes. Remove center membrane, tough fibrous pieces and connective tissue and slice into 3/4-inch thick pieces. Season sweetbreads with salt and pepper and dredge in flour. In a 12 to 14-inch saute pan, heat olive oil until smoking. Saute sweetbreads until dark golden brown on 1 side (8 to 10 minutes). Turn over, add shallots and cook until golden brown (7 to 8 minutes). Remove sweetbreads to a plate and set aside. Add vin santo, tomato paste and rosemary and deglaze pan, scraping the bottom with a wooden spoon. Add the chicken stock and bring to a boil. Replace the sweetbread pieces into the pan and lower heat to a simmer. Cook until liquid is reduced to1/2 cup, add the butter and swirl in. Place shallots onto plate, top with sweetbreads, spoon sauce over and shave truffles over each portion.