Thaw the shanks if frozen, rinse and pat them dry. Liberally dust them with salt and freshly cracked black pepper.
Turn your IP to Sauté high, then add 2 tbsp. of the olive oil. When hot, brown the shanks, two at a time, on all sides. (Add more oil if needed for the 2nd batch.) Remove the shanks from the pot and set aside on a rimmed sheet. Pour out the rendered fat and return the insert to the pot.
Heat the remaining two tbsp. oil in the IP, then add the onions, celery, and carrots. Sauté on high, stirring frequently, until the veggies begin to soften, then add the minced garlic, and stir in the tomato paste.
Add the whole rosemary sprigs, the bay leaf, a dash or two of salt and freshly ground black pepper. Sauté for a few minutes, and then add the red wine.
As the wine simmers, use a wooden spatula to scrape up any bits left on the bottom of the insert, and then pour in the beef stock and the undrained tomatoes.
Nestle the browned shanks into the mixture and pour in any juices that have collected on the sheet pan.
Close the IP and set to high pressure for 50 minutes.
When time is up, allow the pressure to release naturally for 20 minutes, then quick release.
Remove shanks from pot and tent to keep warm.
Set IP on Sauté high, bring to a fast simmer and reduce the liquid for a few minutes to concentrate the juices. Make a slurry from flour or cornstarch mixed with a bit of water and stir into the simmering liquid till thickened to your liking. Adjust seasoning to your taste with salt and pepper.
Serve the shanks whole, one per person, or remove the meat from the bone and mix it back into the gravy and vegetables to serve.
We love this recipe served over mashed potatoes, but egg noodles would be good, too. Enjoy!