Wash grated tapioca in water, drain in a plastic colander until dry, then squeeze out bitter juice using a piece of muslin cloth.
Lightly grease a 23cm square tray with margarine and line with banana leaf.
Melt palm sugar in a wok over a very low heat; add in butter, sugar, tapioca, pumpkin and coconut milk, egg and evaporated milk mixture, salt, corn flour and bicarbonate of soda. Stir well to combine with a hand whisk for 67 minutes.
Pour into prepared tray and bake in preheated oven at 180°C for 5565 minutes or until it is firm and golden and the crust is browned and aromatic.