To make pad thai sauce, heat a small pan on medium low and add fish sauce, palm sugar, tamarind concentrate, and garlic. Cook sauce until palm sugar has completely dissolve. At this point, you will want to taste the sauce and tweek the sweetness or hotness (be careful, the sauce will be hot). To make it more spicy add a little Thai chili powder. Remove from heat and allow to cool 10 minutes before storing it in a jar or plastic container.