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 1/2 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.