Preheat the pressure cooker using the ''Brown'' setting.
Season the veal shanks with salt and pepper and lightly dredge in flour, shaking off any excess. Add the oil to the cooker and brown the shanks on all sides. Remove when brown and set aside.
Cook the onion, carrots, and celery in the cooker for 3–4 minutes. Add the thyme, bay leaf, and oregano and cook for another minute or so. Add the wine and use a wooden spoon to scrape up any brown bits that may have formed on the bottom of the cooker. Bring to a simmer. Add tomatoes, beef stock, and browned veal to the cooker.
Lock the lid in place and cook on ''High'' for 20 minutes. While the veal is cooking, make the gremolata. Chop the orange zest, garlic, and parsley together and combine in a small bowl.
Let the pressure inside the pressure cooker drop naturally after 20 minutes has passed and carefully remove the lid. Season the sauce to taste with salt and pepper, and serve over polenta or risotto with the gremolata sprinkled on top. Serves 6.
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