This is one of the dishes that I will always associate with vacation by the ocean. Not surprisingly it just tastes the best, when one is sitting on the beach, listening to the ocean waves and sipping cold beer.
Make the dipping sauce first. In a mortar pound the garlic with a good pinch of salt. Add the chillis and pound well to create a paste.
Add lime juice, fish sauce and palm sugar. Taste and adjust to your liking. The sauce should be spicy first, then sour, then salty, then sweet.
For the mussels, put the mussels and the herbs into a big pot over high heat. Add a ¼ cup of water to start the steaming process. Cover with a tight fitting lid. Steam in its own liquid for about 8-10 minutes, or until the shells have opened. Shake the pot every now and then during that time to spread the mussels and herbs around.
Discard any unopened mussels. Serve immediately in a big bowl with the dipping sauce on the side.