Heat the oil in a large frying pan over medium heat. Add the beef and cook until browned on all sides, about 5 minutes. Remove from the heat and set aside to rest. In the same pan, add the onion, garlic, ginger, salt and pepper to taste. Cook until the onions are soft and the garlic begins to turn golden brown, 2 to 3 minutes more. Stir in the tomato paste and beef stock. Bring to the boil, then reduce heat to medium-low and simmer, covered, for 30 to 40 minutes, or until beef is tender. Serve with rice and sour cream.