Soak the noodles in room temperature (not cold) water for 30 mins - 1 hour.

Remove seeds from the chilies by using scissors to cut them into chunks and allowing the seeds to pour out.

Grind the chilies in a coffee grinder into a fine powder.

In a mortar and pestle, pound the garlic into a paste, then add the shallots and the ground chilies and pound into a rough paste.

Combine the tamarind paste with the fish sauce and ⅓ cup of water and stir to combine.

Heat a wok or a large non-stick skillet over medium heat. Once hot, add the oil and the chili paste and cook for about 1 minute, stirring constantly.

Add the palm sugar and cook until mostly dissolved, about 30 seconds. Then add the tamarind sauce mixture and bring to a boil.

Add the shrimp (if using) and cook them in sauce for 1 minute, flipping them halfway through, just until they are done. Turn off the heat and remove the shrimp, leaving all the sauce behind.

Turn the heat back on medium high and add the soaked noodles. Keep tossing the noodles with tongs until all the sauce has been absorbed.

Once the noodles are cooked, add the beansprouts, garlic chives, cooked shrimp and most of the crab (if using), leaving a bit of crab behind for garnish. Turn off the heat and toss everything until just until the beansprouts are wilted.

Plate the noodles, top with more crab (if using), more beansprouts, cucumber, and a lime wedge on the side.