Boil the dried mushrooms in a wok or saucepan of water for 15 to 20 minutes until tender, then drain through a sieve, squeezing out any excess water, and set aside. Soak the vermicelli in hot water for 2-3 minutes until tender, then drain and refresh in cold water. Drain again and spread out on a clean towel to dry for 10 minutes, then chop into bite-sized pieces.
Heat 1 tablespoon of oil over medium heat and lightly fry the onion for 1 minute, then set aside to cool. Place the minced meat in a small bowl and massage in the fish sauce and sugar.
Separate 3 eggs. Place the yolks in a small bowl with 1 teaspoon of vegetable oil, and the whites in a mixing bowl. Break the remaining 5 whole eggs into the bowl with the whites, beat well and season with salt and pepper. Remove as many bubbles from the beaten egg as possible using the edges of a clean sheet of parchment.
Add the chopped vermicelli, sliced mushrooms and fried red onion to the mixing bowl with the whole eggs and stir well, then add in the marinated meat, breaking it up with your hands and mixing it through. Line a heatproof bowl or a loaf tin with parchment and pour in the meat mixture. The mixture should be 2½ to 2¾ inches deep and the bowl or tin should fit into your steamer. (If you don't have a steamer, roll three sheets of aluminum foil into baseball-sized balls and place in the bottom of a pot and pour in about an inch of water.)
Steam meatloaf for 25 minutes. Carefully lift the lid off the steamer and pour the beaten egg yolks over the top of the eggy meatloaf, completely covering the surface. Continue to steam for another 5 minutes, then slice and serve with crunchy vegetables and mint sprigs.
