1In medium bowl, mix 1 tablespoon of the oil, the garlic, gingerroot, pepper, coriander and beef. Cover and refrigerate 30 minutes or up to 8 hours.
2In 12-inch skillet (preferably nonstick), heat remaining 3 tablespoons oil over medium-high heat until shimmering and hot. Add marinated beef. Cook 6 to 8 minutes, stirring constantly so garlic doesn’t burn, until beef is browned and cooked through. Drain fat.
3In small bowl, mix sugar, lime juice, 2 tablespoons fish sauce and the vinegar. Add mixture to skillet with beef. Stir and heat to boiling. Watch carefully as liquid evaporates to avoid scorching. When only about 1 tablespoon liquid is left, use slotted spoon to remove beef to bowl; cover to keep warm.
4Add onion to skillet and cook 1 minute, stirring frequently. Stir in lemongrass, garlic and chile. Cook 30 seconds, stirring constantly. Add broth, 2 tablespoons fish sauce and the oyster sauce. Heat to boiling, stirring occasionally. Reduce heat to medium and simmer 1 minute longer. Return beef to skillet and cook 30 seconds, stirring constantly. Serve with rice.