Heat oil. Add butter. When butter starts to foam add beef to pan.Cook until all liquid has evaporated. Stir in onions,garlic,ginger,saffron,cumin,salt and pepper.Cook until almost dry. Add half cup water, cover pan, turn down heat and simmer for 2 hours adding more water as needed. When beef is tender add prunes and cook 10 mins more. Check seasonings. Serve hot sprinkled with sesame seeds. I serve it with couscous mixed with chickpeas.