Turn Instant Pot to “Saute”mode and heat oil.
Season the lamb shanks with salt and pepper.
Add them in the pressure cooker and brown them on each side. If the pot is too crowded, work in batches.
Remove lamb from the pot and keep aside.
Heat butter on the "Saute" mode.
Add onions, garlic, carrots, celery, cinnamon stick and cook for 4-5 minutes or until veggies are partially softened and fragrant.
Add the shanks back in the pot.
Add broth, tomato paste, red wine, Italian seasoning, paprika, cumin powder, turmeric powder, salt, pepper, fresh thyme, rosemary, bay leaves.
Mix until combined.
Put the lid on and turn the the valve to “Sealing.” Select “Manual” mode and set the timer for 60 minutes.
When the cook time is over, let the pot sit undisturbed and allow the pressure to release naturally.
Remove the lid and gently transfer the shanks onto a plate. They should be very tender. Cover with foil to keep them warm.
Discard cinnamon stick, bay leaves and springs of rosemary and thyme.
Turn on the "Saute" mode and cook the gravy until it's simmering.
Then, thicken gravy by dissolving cornstarch and water to make a slurry and pour that in the pot, while gently stirring.
Continue cooking on this mode until liquid is reduced to your desired thickness.
Add the lambs back in the pot and coat it with the thick gravy.
Serve with mashed potatoes. Enjoy!