Put water chestnut in a ziplock bag and pressed with the side of a chopping knife. Set aside.
Dissolve water chestnut flour in 1.5 cups water and sieve to remove impurities.
Boil brown sugar in 2.5 cups water until sugar dissolved. Turn off heat. Sieve to remove impurities.
Bring sieved sugar water back to boil. Add pressed water chestnuts. Cover the lid and boil for 5 minutes. Note carefully to prevent spilling. Then add 1.5 tablespoons oil and mix.
Mixed water chestnut water thoroughly. While mixing add in hot sugar water with water chestnuts.
Continue to mix until it turns into a smooth paste.
Pour the paste into the oiled cake tin and steamed for 50 minutes.
Done.
Cooled before unmold. Can have it cold, warm or fried.