Preheat your oven to 300°F.
In a small bowl, mix together the minced garlic, rosemary, olive oil, salt, and black pepper to create a paste.
Rub the garlic and herb mixture all over the lamb shoulder, ensuring it is well coated.
Place the lamb in a roasting pan and pour the broth and lemon juice around it.
Cover the roasting pan tightly with aluminum foil.
Roast in the preheated oven for 4 to 5 hours, or until the meat is tender and easily pulls apart with a fork.
In the last 30 minutes of cooking, remove the foil and brush the lamb with Dijon mustard for added flavor.
Once done, remove the lamb from the oven and let it rest for 15 minutes before slicing.