Pat veal shanks dry with paper towels. Season generously with salt and pepper on all sides. Dredge lightly in all-purpose flour, shaking off excess. (About 10 minutes)

Heat olive oil and butter in a Dutch oven over medium-high heat. Brown shanks in batches for about 4 minutes per side until golden and crispy. Set aside. (15 minutes)

In the same pot, sauté onion, carrots, and celery over medium heat until softened and fragrant, about 8 minutes. Add minced garlic and cook for 1 more minute. (10 minutes)

Pour in white wine to deglaze the pot, scraping browned bits from the bottom. Simmer and reduce by half, about 5 minutes. (5 minutes)

Stir in crushed tomatoes. Return browned shanks to the pot, nestling them in the sauce. Add broth to come halfway up the meat. Toss in thyme sprigs and bay leaves. Season lightly with salt and pepper. (5 minutes)

Bring to a gentle simmer, cover, and transfer to a preheated 325°F (160°C) oven. Braise for 2 to 2.5 hours until meat is fork-tender. Check halfway through and spoon sauce over shanks. (2 to 2.5 hours)

While braising, combine parsley, lemon zest, minced garlic, and olive oil in a bowl to make gremolata. Mix well and set aside. (5 minutes)

Remove pot from oven, discard thyme stems and bay leaves. Spoon sauce over shanks, sprinkle with gremolata, and serve immediately with risotto or polenta. (5 minutes)