Moroccan Mechoui (Slow Roasted Leg of Lamb or Shoulder)

Name: Moroccan Mechoui (Slow Roasted Leg of Lamb or Shoulder)
Prep time: 15 min
Cook time: 8 h
Total time: 8 h 15 min
Cuisine: Moroccan
Ingredients: 1 whole leg of lamb (bone-in or shoulder); 4 tablespoons unsalted butter , room-temperature; 3 or 4 cloves garlic , pressed; 2 teaspoons kosher salt (or to taste); 1 teaspoon freshly ground black pepper (or to taste); 1 teaspoon cumin; 1/2 teaspoon saffron threads , crushed; 1/4 teaspoon turmeric; 1 tablespoon olive oil; Salt for dipping, for garnish; Cumin for dipping, for garnish