If you can't find veal cheeks, use about 3 pounds of short ribs instead. For fall-off-the-bone tenderness, add 1 hour to the braising time.
Preheat oven to 325°. Combine breadcrumbs and next 3 ingredients. Set aside.
Sprinkle veal cheeks with salt and pepper. Heat oil in an ovenproof Dutch oven over medium-high heat. Cook veal cheeks, in two batches, 3 to 4 minutes on each side or until browned. Remove from pan.
Reduce heat to medium, and add onion and next 3 ingredients. Cook vegetables 5 minutes or until browned. Add thyme, bay leaf, and peppercorns. Add white wine, stirring to loosen particles from bottom of pan, and cook 2 minutes. Add veal stock, and bring to a boil. Remove from heat. Return veal cheeks to pan.
Bake, covered, at 325° for 1 1/4 hours. (Veal cheeks are done when a small knife inserted in the middle slides out with no resistance.) Remove veal cheeks from pan; keep warm. Strain braising liquid, return liquid to pan, and reduce over medium-high heat to about 2/3 cup.
Place veal cheeks on a roasting pan, and brush with mustard; sprinkle with herbed breadcrumbs. Broil 1 to 2 minutes or until golden brown. Serve with reduced braising liquid.