Preheat the oven to 325 degrees F. Season the lamb with salt and pepper. Heat the oil in a Dutch oven or ovenproof pot set over medium-high. Cook the lamb until nicely browned. Add the onion and garlic to the pot and cook 3-4 minutes more. Sprinkle in the flour and mix well. Slowly, stirring constantly, mix in the stock. Mix in the rosemary and bring to a simmer. Cover and cook in the oven for 45 minutes. Stir in the potatoes and cook 30 minutes more, or until cooked through. Stir in the asparagus and cook a few minutes more to heat it through. Adjust seasoning and serve.
Note: To blanch the asparagus, plunge into boiling water for 2 minutes. Drain well, cool in ice-cold water, drain well again and pat dry.