Cut the beef into roughly 1 inch cubes. In a medium sized bowl, combine the fish sauce, soy sauce, sugar, and pepper. Add the beef and stir to combine. Ensure that the beef is well coated in the marinade. Marinate for at least 30 minutes, or overnight for best results.
Add the other tablespoon of garlic and continue to shake the pan until the beef is cooked to desired doneness. The beef will taste better if it is still a little rare.
Remove from heat. Serve hot.
Recipe by The Little Chef at http://littlechefblog.com/shaking-beef/