In a small saucepan combine milk and bread crumbs and bring to a boil over high heat. Boil 2 to 3 minutes until very thick. Transfer to a large mixing bowl. Skin chorizo, mince half and coarsely chop remainder. Add to bread-crumb mixture. In a skillet over medium heat saute onion in butter until tender, about 5 minutes. Add to bread-crumb mixture along with egg. Beat vigorously and season with salt and pepper.
Cut 8 18-inch-long pieces of butcher's twine. Place boned veal breast, cut side up, with longer side facing you (longer side will be about 18 inches.) Season with salt and pepper. Mound stuffing in middle third of veal breast, leaving 1 inch uncovered on each side. Roll breast from bottom, pulling meat over stuffing to form a cylindrical stuffed package. Tie tightly at each end to enclose filling; tie firmly at 2-inch intervals to ensure that flap stays closed during cooking. Season well with salt and pepper, and coat lightly with flour.
Preheat oven to 325 degrees. In a large, deep, very heavy gauge roasting pan at least 18-inches long, with sides higher than veal breast, or a dutch oven, heat olive oil over medium-high heat. Add 5 of the reserved veal bones, the quartered onions, carrots and bell peppers; saute until vegetables begin to brown, about 10 minutes. Push bones and vegetables to sides of pan, increase heat to high and add stuffed roast. Brown veal on all sides, about 10 minutes in all. Add enough wine and beef broth to reach halfway up sides of veal breast (you may not need to use all the wine and broth; however, if your pan is very large, you may need to add some more.) Bring liquid to a boil, then reduce heat to a bare simmer. Cover pan with lid or with aluminum foil; transfer to oven and cook 3 hours, checking occasionally to make sure liquid is gently simmering.
Remove veal from pan to a cutting board and cover loosely with aluminum foil to keep warm. Taste braising liquid: if it needs to be intensified, season well with salt and pepper and boil over high heat until reduced and flavorful. Discard veal bones. Remove strings and slice veal breast in 1/2-inch slices. Serve veal, sauce and braising vegetables, with garlicky potatoes or rice.