Tender braised veal shanks surround a rich repository of bone marrow in this traditional Italian osso buco dish. Serve with Risotto Milanese.
Preheat oven to 350 degrees.
Heat vegetable oil in a large Dutch oven over medium-low heat until very hot. Place flour in a shallow dish. Season veal shanks with salt and pepper; dredge in flour, shaking off excess. Working in batches if necessary, add shanks to Dutch oven (they should sizzle immediately). Cook, turning, until browned on all sides, 10 to 15 minutes. Remove veal shanks from Dutch oven and set aside.
Add onion, carrots, celery, and leek to Dutch oven; cook, stirring, until softened and lightly browned, 8 to 10 minutes. Add bay leaf, thyme, oregano, tomatoes, wine, and stock. Return veal shanks to Dutch oven and bring to a simmer. Cover and transfer to oven; cook, checking occasionally to make sure the liquid is still simmering, until meat is very tender, about 2 1/2 hours.
Remove from oven and transfer shanks to a platter; cover with parchment paper-lined aluminum foil to keep warm. Place Dutch oven over medium heat; simmer until sauce is thickened, about 15 minutes. Season with salt and pepper. Return shanks to Dutch oven to heat through and coat with sauce. Sprinkle with chopped parsley and lemon zest; serve.