Soak the mushroom stems in water until soft (at least 2 hours) and trim off the lower ends.
Cut the beancurd sheets into strips. Separate the strips with your fingers (it's important that they don't stick to each other)
Bring 8 cup of water with the sodium carbonate to a boil, add the beancurd strips and let simmer over very low heat for 10 to 15 minutes (do not boil!) The strips should swell like noodles and the color turn white.
Add 1 tbsp salt and stir carefully. Place a cheesecloth in a strainer and pour the beancurd strips on the cheesecloth. Rinse by pouring 10 cup boiling hot water over it. (this takes away the taste of the sodium carbonate and the salt)
Wrap the cheesecloth around the mass and shape it into a square form. Place a heavy weight on it for 5 minutes. Remove the cheesecloth and cut the beancurd into 1.5cm thick "chicken" slices. Deep-fry in oil (180°C) until golden brown.
Fry 'A' in 2 tbsp oil over high heat until fragrant. Add the chicken slices and cook for 5 minutes until there is hardly any liquid left. Sprinkle a few drops of sesame oil over it and remove.
Cut into thin slices and arrange on a plate.
It's very important that you do not boil the beancurd strips, otherwise they will dissolve.
The purpose of adding salt is to make the beancurd strips stick together more easily when shaping the mass into a square form.