Heat 2 tbsp of oil in a large cast-iron pot. Season the shanks with pepper and salt and brown them on both sides. Do this in two batches if the pot is not large enough.
Meanwhile, finely chop the carrots, onion, celery, and leek.
Toast the fennel seeds in a dry pan until they lightly color and become aromatic. Crush coarsely in a mortar.
Remove the shanks from the pot and add extra oil. Sauté onion, garlic, and fennel seeds. Then add carrot, celery, and leek and let simmer for 10 minutes.
Deglaze with the port, add brown stock and diced tomatoes. Season with pepper and salt and add thyme and bay leaf.
Return the shanks to the pot, ensuring they are submerged in the sauce, and let simmer for at least an hour. Check regularly and add broth if necessary.
The dish is ready when the meat falls off the bone. Remove the marrow, season with fresh pepper and fleur de sel.
Shred the meat and mix it into the sauce.
Cook the pasta according to the package instructions.
Serve the ossobuco on the pasta, finished with marrow, cheese, and parsley.
Tips
Add a dash of lemon juice to the sauce for a fresh touch. Replace Paccheri pasta with another sturdy pasta such as Rigatoni or Penne.