This is a classic dish of shanks braised in white wine and tomatoes - a traditional northern Italian dish. Osso Bucco are rich in marrow. Consider including smalls spoons at the tale so your guests can enjoy the bone marrow.
Spread the flour in a shallow dish suitable for dredging.
Tie Thyme, Rosemary and Bay Leaves together using kitchen twine.
Season the Shanks with salt and pepper to taste, then dredge in flour doing your best to coat all of the surfaces of the shanks.
Heat a tablespoon or so of olive oil in your pressure cooker, or whatever pot you are using. Sear the shanks in the oil, doing your best to brown all sides, achieving a golden brown color. You will need to do this in batches to ensure a high temp for browning. As you complete the browning of each shank, remove and set aside for now.
After all the shanks have been browned, turn the heat down to medium. Add the butter to the pan. Once the butter has melted, stir in the onions, carrots and celery. Cook until the vegetables are soft - about 8 minutes. Stir in the garlic and tomato paste and cook another 1-2 minutes.
Add the white wine to the pot to deglaze it, scraping and crispy bits from the bottom. Stir in the stock and the diced tomatoes and ring to a simmer.
Once the sauce is simmering, place the shanks back into the sauce doing your best to semi-submerge them. If preparing in a Pressure Cooker, seal the Pressure Cooker and place on high. Once up to pressure, cook for 40 minutes - then turn off the heat and let the pot return to normal pressure on it's own. If cooking in a dutch oven or slow cooker, plan to cook for approximately 4 hours. You.can place your oven proof pot in the oven at 325℉.
While your shanks are cooking, prepare the Gremolata by combining the parsley, lemon zest, garlic and salt. Set aside until ready to serve.
Once your pressure cooker has de-pressurized, carefully remove the shanks to a warm serving platter. Meanwhile, simmer the sauce to reduce it. Stir often while the sauce gets thick. This will take about 10-15 minutes. While the sauce reduces, taste and adjust salt and black pepper as needed. After reducing, let the sauce rest for 8-10 minutes. You have the option, at this stage, to skim fat off the sauce if you wish.
Have 4 warm plates at the ready. Place one shank on each plate. Top with a generous helping of sauce and a sprinkle of Gremolata, with extra Gremolata on the side in case diners want more. You may also want to provide diners with a small spoon for scooping marrow out of the shank bones.
This dish pairs well with polenta and/or crusty italian bread.