Slow cooked lamb shoulder with boulangere potatoes

Name: Slow-cooked lamb shoulder with boulangere potatoes
Ingredients: 3 medium onions, thinly sliced; 6 large waxy potatoes, peeled and thinly sliced; 1 bunch thyme, leaves picked; Salt and black pepper; 1 whole lamb shoulder; 1 garlic bulb, peeled and separated into cloves; 568ml/1 pint chicken stock; Cooked french beans (or other green vegetables), to serve