Preheat your oven to 325°F (160°C).

In a small bowl, combine the ground star anise, cracked cardamom, salt, and black pepper. Mix well to create a spice rub.

Pat the lamb shoulder dry with paper towels. Rub the olive oil all over the lamb, then coat it generously with the spice mixture, ensuring it is evenly covered.

In a large oven-safe skillet or Dutch oven, heat a tablespoon of olive oil over medium-high heat. Once hot, sear the lamb shoulder on all sides until browned, about 5-7 minutes per side. Remove the lamb and set aside.

In the same skillet, add the chopped onion and minced garlic. Sauté until the onion becomes translucent, about 3-4 minutes.

Pour in the beef or lamb stock, scraping up any browned bits from the bottom of the skillet. Add the honey and balsamic vinegar, stirring to combine.

Return the lamb to the skillet, nestling it into the liquid. Cover with a lid or foil and transfer to the preheated oven. Roast for 3-4 hours or until the lamb is fork-tender.

While the lamb is roasting, prepare the caramelized leek butter. In a separate skillet, melt the unsalted butter over medium heat. Add the sliced leeks and cook, stirring occasionally, until they are soft and caramelized, about 10-15 minutes. Season with salt and set aside.

Once the lamb is done, remove it from the oven and let it rest for at least 15 minutes before slicing.

To serve, slice the lamb shoulder and drizzle with the pan juices. Spoon the caramelized leek butter over the top and garnish with fresh herbs.