It's quite difficult to find a truly authentic pad Thai outside of Thailand and there are some ingredients that can be hard to find. In Thailand, pad Thai typically has tamarind paste, dried shrimp, bean curd (pressed tofu), sweet preserved radish, and garlic chives. Your local grocery store might not have all those. Some restaurants serve a very Westernized version (think tomato ketchup in place of the sauce and way too much sweetness). This recipe is fairly authentic but definitely very tasty!