Preheat your oven to 350°F (175°C). Season the lamb shanks generously with salt and black pepper.

In a large Dutch oven or heavy pot, heat the olive oil over medium-high heat. Add the lamb shanks and sear on all sides until browned, about 3-4 minutes per side. Remove from the pot and set aside.

In the same pot, add the sliced fennel and chopped onion. Sauté for about 5-7 minutes, until they start to soften. Stir in the minced garlic and crushed black peppercorns, cooking for an additional minute until fragrant.

Pour in the balsamic vinegar, scraping up any brown bits from the bottom of the pot. Add the beef stock, thyme, rosemary, and brown sugar. Stir to combine. Return the lamb shanks to the pot, ensuring they are submerged in the liquid. Bring to a simmer, then cover and transfer to the preheated oven. Braise for 2 to 2.5 hours, or until the lamb is fork-tender.

While the lamb is braising, prepare the parsnip gravy. In a pot, add the chopped parsnips and cover with water. Bring to a boil and cook until tender, about 15 minutes. Drain the parsnips and return them to the pot. Add the butter and vegetable stock. Mash until smooth. If desired, stir in the heavy cream for extra richness. Season with salt and pepper to taste.

Once the lamb is done, remove it from the oven and let it rest for a few minutes. Strain the braising liquid to separate the solids, then return the liquid to the pot and simmer until slightly thickened.

Plate the lamb shanks over a generous scoop of silky roasted parsnip gravy. Drizzle with the thickened balsamic glaze from the pot. Enjoy!