Place tamarind paste, fish sauce and palm sugar into a sauce pan.
¾ Cup Tamarind Paste, ¾ Cup Fish Sauce, ¾ Cup Palm Sugar
Heat up the pan and keep over a medium to low-heat setting. Stir the ingredients together.
Mix up the sauce well and let the sauce simmer on a low-heat setting slowly for a couple of minutes so that all the germs are killed in the heat. *see Notes
Bottle up the sauce when done reducing.
Store in your fridge or freeze in small ice cube tray batches.
Video
Notes
Use Thai tamarind paste not Indian tamarind paste. Thai one is thinner and less sour, on the sweeter side. Indian one is thicker and way more sour. Yet, if you want to experiment or if you can only get Indian Tamarind, then use that simply.
Try to use Thai Palm or Cane Sugar. You can use Asian Jaggery or South American Panela, Piloncillo or Rapadura. You can use crumbled or block or cone-shaped cane/palm sugar.
Likewise, you can make this Pad Thai sauce vegan by using soy sauce instead of fish sauce. If you are not into a vegan lifestyle, then stick to your fish sauce, of course!
The ratio is 1:1:1, which makes it easier for you to prepare this sauce in bigger or smaller quantities. You just need to make sure that all the ingredients are perfectly balanced. For example, when you use thick Indian tamarind paste (which ideally you shouldn't), the sauce will turn more sour and thick. In that case, you will need to adjust the sauce by adding a little more palm sugar and fish sauce. So make sure to taste test your sauce before bottling it up.
You can also cook it down further to a thicker consistency to save space in your fridge. I prepare my pad thai sauce to a honey-like consistency so that I can take out a spoon full easily.