Heat 2 tablespoons of olive oil in a large Dutch oven over medium heat. Dredge the veal shanks in flour, shake off the excess and sear them in the Dutch oven until they are well browned, about 5 to 8 minutes. Set the shanks aside on a plate.

Add the remaining olive oil, to the pot over medium heat and stir in the celery, carrots and onions. Cook for 4 minutes until the onions begin to brown. Stir in the garlic. Pour in the beef stock and deglaze the pan by scraping the brown bits from the bottom, using a wooden spoon.

Add the veal shanks to the pan followed by the Marsala wine, tomatoes, salt and pepper, to taste, and the thyme. Simmer for 10 minutes, then cook slowly over low heat for 1 hour and 45 minutes.

Gremolata: Combine the parsley, lemon zest, and garlic in a food processor. Roughly chop and set aside.

Arrange the veal shanks on a bed of rice, risotto, or mashed potatoes. Garnish each serving with a tablespoon of gremolata and serve.