Prepare your cilantro roots by washing them and scraping the outer skin and rootlets away from the main tap root. Slice the garlic into smaller pieces. Place the prepared cilantro roots and garlic in a mortar and pestle and pound into a smooth paste.
Next slice the Thai chilis into smaller pieces, place into the mortar and pestle, and pound until they are incorporated into the paste.
Add the fish sauce, lime juice, and palm sugar to your mortar and stir with the pestle until the palm sugar is dissolved and a homogeneous sauce has been formed. Taste and adjust the seasonings according to your personal preferences.
Before serving, top with fresh cilantro leaves. Enjoy with your next seafood dish, whether it be steamed crab or grilled lobster!