Been meaning to put this one up for a while now, just haven't gotten around to making it myself! So just like everything else, the real thing is completely different and a hell of a lot better than what you'll buy in the shop, and making it is really simple + easy.
Ingredients are:
2-4 Red Chilies
3 Coriander Roots + few leaves to garnish at the end with
4 Cloves of Garlic
1 Tsp Salt
1/2 a Cup of Coconut Vinegar
1/2 a Cup of Water
1 Cup of White Sugar (or Castor Sugar)
1 Tbsp of Fish Sauce

First off, stick the chilies, coriander root, garlic + salt, all chopped up, into the mortar and pound it up a bit, doesn't have to be a paste, but mashed up a fair bit. I use 1-2 big red chilies for the flavor and 2 small chilies for a bit of heat. Be sure to wash the coriander roots, and scrape them a bit with the knife to get off some of the furry shit on the outside.

Then, stick this in a saucepan, and add the sugar, coconut vinegar and water and put over medium/high heat. Stir it regularly, to stop the sugar from burning on the bottom. Bring it to a light boil, and then let it simmer for 5-6 minutes, stirring as you go. Can always leave it a bit longer if you feel it needs it, but don't expect it to get anywhere near the texture of "sweet chili sauce" you buy in the shops. It'll still be pretty much water consistency when you're done, the way it should be.

Take it off the heat, and add the tablespoon of fish sauce. Might need to stir it for the first minute or two, just to make sure that it doesn't burn on the bottom, and then leave it for a while. If you're making it to use straight after, chop up some coriander and add it in just before you serve, otherwise just wait until it's cool, add it in and stick it in whatever airtight jar you got. Vinegar - it'll keep, might wanna keep it in the fridge just to be safe but up to you. I usually go through it within a couple of weeks of making it, so never tried keeping it for a long time, so I don't know if the coriander leaves will cause any problems being stored for ages? Anyone got a clue on that one? Will the vinegar stop them from killing your family?

And there you have the best friggen sweet chili sauce you'll ever have. It's delicious. Let me know how it goes!
~Sydes