Put the mushrooms in a bowl, cover with water and soak for 20 minutes, then drain and thinly slice.
Soak the bean thread vermicelli in water for 20 minutes, then drain and cut into 1 1/2-inch/4 cm lengths.
Place the sliced jicama in a muslin cloth and squeeze out its juice, then discard.
In a large mixing bowl, combine the mushrooms, vermicelli, jicama, pork, crabmeat, onion, sugar, 2 teaspoons sea salt, 2 teaspoons white pepper, and fish sauce.
Knead the mixture in the bowl for 10 minutes, or until your arms get tired.
Working with one rice paper at a time, submerge the rice paper in a large pan of warm water, then transfer it to a chopping board or work surface.
Take 1 1/2 heaping tablespoons of the mixture and place it on the bottom edge of the rice paper. Fold the 2 adjacent sides, one on top of the other, into the center.
Roll the apex to form a nice firm roll, and secure with a dab of beaten egg white. Repeat until you have filled all the rice papers.
Pour the oil into a wok and heat to 350 degrees F/ 180 degrees C, or until a cube of bread dropped into the oil browns in 15 seconds.
Fry the parcels in 3 batches for 6 minutes, or until lightly browned and crisp.
Evenly distribute the rice vermicelli noodles among 4 to 6 bowls, top with sliced herbs, then cut the parcels into the bowls.
Pour 2 tablespoons nuoc cham into each bowl and garnish with fried shallots and peanuts.