Prepare the paste: Place the fresh chilies in the mortar and begin to pound them with the pestle. Pound until the chilies are well-bruised and have released some of their juices.
Add the garlic: Add the peeled garlic cloves to the mortar with the chilies. Continue to pound and grind until you have a coarse paste. Do not over-process; a slightly chunky texture is desired.
Mix in the wet ingredients: Transfer the chili and garlic paste to a small bowl. Add the sugar, fish sauce, and fresh lime juice.
Stir and dissolve: Use a spoon to stir the mixture vigorously until the sugar is completely dissolved. If you're using palm sugar, you may need to break it down into smaller pieces first to help it dissolve.
Taste and adjust: This is the most important step. Taste the sauce and adjust the flavors to your liking.
For more sourness: Add a little more lime juice.
For more sweetness: Add a little more sugar.
For more saltiness: Add a little more fish sauce.
For more spiciness: You can mince an additional chili and stir it in.
Serve: This sauce is best served fresh. It pairs wonderfully with grilled seafood like crab, squid, or fish, as well as grilled steak or chicken.