1. In a large soup pot, heat the olive oil and butter over moderately low heat. Add the garlic, onions, carrots, half the rosemary, the thyme, and salt and pepper to taste. Simmer, Add the lamb stock, tomatoes, lentils, bay leaf, and the lamb bone from the roast if you still have it and bring the soup to a boil. Reduce the heat and simmer, partially covered, for about 40 to 50 minutes, or until the lentils are tender. Taste for seasoning.

2. To serve, place a small handful of cooked lamb in the bottom of each soup bowl and ladle the hot soup over it. Garnish with the remaining fresh rosemary. Serve with a bottle of Tabasco on the side.