Step 1: Prepare the Beef Shanks

1. Pat the beef shanks dry with paper towels to remove excess moisture. This ensures they sear properly.
2. Season both sides of the shanks with salt and pepper, then lightly dredge them in flour, shaking off any excess.

Step 2: Sear the Shanks

1. Heat 2 tablespoons of olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat.
2. Add the beef shanks to the pot and sear for 4-5 minutes on each side, or until golden brown. Work in batches if needed to avoid overcrowding. Remove the shanks and set them aside on a plate.

Step 3: Sauté the Vegetables

1. Reduce the heat to medium and add the remaining tablespoon of olive oil to the pot.
2. Add the diced onion, carrot, and celery. Sauté for 6-8 minutes, or until softened and lightly caramelized.
3. Add the minced garlic and cook for another minute, stirring frequently.

Step 4: Deglaze the Pot

1. Pour the white wine into the pot, scraping up any browned bits from the bottom with a wooden spoon. These bits add incredible flavor to the sauce.
2. Let the wine simmer for 2-3 minutes to reduce slightly.

Step 5: Build the Braising Liquid

1. Stir in the diced tomatoes, tomato paste, and broth. Add the thyme, bay leaf, and rosemary sprig.
2. Return the seared shanks to the pot, ensuring they’re partially submerged in the liquid.

Step 6: Braise the Osso Buco

1. Bring the liquid to a gentle boil, then reduce the heat to low. Cover the pot with a lid and transfer it to a preheated oven at 325°F (160°C).
2. Braise for 2 to 2 1/2 hours, or until the beef is tender and the marrow is soft. Check occasionally and add more broth if the liquid reduces too much.

Step 7: Prepare the Gremolata

1. While the Osso Buco is cooking, mix the lemon zest, parsley, and minced garlic in a small bowl. This fresh, zesty topping will brighten the dish.

Step 8: Serve the Osso Buco

1. Remove the pot from the oven and discard the bay leaf and rosemary sprig.
2. Plate the beef shanks and spoon the sauce generously over the top. Sprinkle with gremolata if desired. Serve with your preferred side dish and enjoy!