To make the rolls: Soak the transparent vermicelli in warm water for 15 to 20 minutes, cut them into 2-inch segments, and drain. Soak the dried black mushrooms in warm water for 30 minutes, drain, and cut into julienne. Mix all the filling ingredients. Shape the imperial rolls by forming a portion of the filling into a finger shape and placing it in the center of a pastry sheet, which you will have placed in front of you in the shape of a diamond. First, fold in the corners on each side towards the center, then fold in the nearest point over the two previous points. Just moisten the last point with a little egg yolk and close the roll fairly tightly. Fry for about 5 minutes.
For the nuoc nam sauce: Mix all the ingredients without cooking.