1 - Heat the vegetable oil in a large frying pan over medium-high heat.

2 - Add the lamb and cook until browned on all sides, about 5 minutes.

3 - Season with saffron, salt and pepper to taste; stir in all but 4 tablespoons of the onion, and pour in the water.

4 - Bring to the boil, then cover, reduce heat to medium-low, and simmer until the lamb is tender, about 15 minutes.

5 - Uncover the pan, stir in the butter and allow the sauce reduce 5 to 10 minutes to desired consistency.