Preheat your oven to 325°F (160°C).

Season the lamb shoulder generously with salt and black pepper. In a large Dutch oven, heat the olive oil over medium-high heat. Once hot, add the lamb shoulder and sear on all sides until browned, about 4-5 minutes per side. Remove the lamb from the pot and set aside.

In the same pot, add the diced onion and cook for about 5 minutes until softened. Stir in the roasted garlic and cook for an additional minute until fragrant.

Add the chopped plums to the pot and stir to combine. Pour in the red wine, scraping the bottom of the pot to release any browned bits. Bring the mixture to a simmer and let it cook for 5 minutes.

Return the lamb shoulder to the pot and add the lamb stock, carrots, parsnips, celery, thyme, rosemary, and bay leaf. Bring the mixture back to a simmer.

Cover the pot and transfer it to the preheated oven. Braise for 3 to 4 hours, or until the lamb is tender and easily pulls apart with a fork.

Once done, remove the pot from the oven and carefully take out the lamb shoulder. Transfer it to a cutting board and let it rest for 10 minutes.

Meanwhile, strain the braising liquid into a saucepan, discarding the solids. Bring the liquid to a boil and reduce it by half over medium heat, about 10-15 minutes.

Stir in the balsamic vinegar and honey. Adjust seasoning with salt and pepper if necessary.

Slice the lamb shoulder and serve it with the rich root vegetable gravy drizzled on top.