Mash beancurd through a wire mesh sieve into a large bowl. Discard any coarse dregs. Add egg yolk, salt, self-raising flour and mushrooms. Blend to a smooth paste.
Heat a wok with enough oil until fairly hot over medium heat. Dip 5 Chinese soup spoons into the hot oil. Remove and add the prepared beancurd paste. Level it off with a palette knife. Once the oil is hot enough hold the handle of a spoon and lower it into the oil. Allow the paste to slip out into the oil. The beancurd will form a pi pa (a traditional Chinese instrument) as it enters the oil. If it is stuck to the spoon, use a knife to lightly loosen the paste from the spoon. Repeat with the other spoons.
Deep-fry the pieces for 3-4 minutes. Turn the pieces over until they are golden and float. Remove from the oil.
Dip the pi pa tofu pieces in chilli sauce if preferred.