Prep the oven: Preheat oven to 350°F.
Sear the shanks: Heat ½ the olive oil in a large dutch oven over medium-high heat. Add as many lamb shanks as can fit on the bottom of your pot and season them with salt and pepper. Sear for about 5 minutes or until browned. Flip, season with salt and pepper, and sear the other side. Remove the shanks from the pot and set aside. Repeat with remaining oil and shanks.
Add veggies: Add the onion, carrots, celery, season with salt and pepper, and saute for 3-5 minutes or until the onion becomes translucent. Mix in the garlic and tomato paste well, then saute for another minute.
Make the sauce: Pour in the entire bottle of passata. Add about ½ cup of beef broth to the passata bottle, screw the lid back on, and shake to get all the excess passata from the sides of the bottle. Add this to the pot along with the remaining beef broth. Pour in the bottle of wine and stir everything to combine. Add the thyme, rosemary, bay leaves, cinnamon sticks, and let everything come to a simmer.
Add shanks back and cook: Add the shanks back to the pot and arrange them so they are fully submerged. You can top them with more broth if needed. Cover the pot with a lid, and braise in the oven for 2 hours. Remove the lid, and braise for another 30 minutes.
Finish the sauce: Remove the shanks from the pot. Strain the liquid into a saucepan using a sieve. Bring the liquid to a simmer and reduce by half, about 10 minutes. You can add a cornstarch slurry (equal parts cornstarch and water) to the sauce, 1 tsp at a time, if you want it to be thicker. Season to taste with salt and pepper.
Serve: Spoon a small amount of sauce over the shanks to serve and leave the rest in a gravy boat on the side.