Put mustard seeds, vinegar, and a dash of water into the blender and blend until seeds are crushed. Set aside. Heat oil in skillet. Brown onions, garlic and ginger. Add curry powder and beef. Stir over medium heat until well browned about 5 minutes. Stir in cloves, cardamom, cinnamon, turmeric, black pepper, and curry leaves. Add water and mustard seed blend. Stir well. Simmer until sauce is thick.