Soak Water Chestnut Flour (115 gram)and Water (250 milliliter) together, stir well and set aside for later use.
In a pot, boil Water (500 milliliter) with Rock Sugar (125 gram) together until sugar dissolved. Add dried Dried Osmanthus Flowers (1 tablespoon) to the water and bring to a boil again. Turn off heat and cover pot with lid for 10 minutes. Remove some osmanthus flowers.
Strain water chestnut liquid (step 1 ) through a fine sieve.
Bring osmanthus liquid to boil, pour in the chopped Water Chestnuts (4) and stir well. Lower heat and pour water chestnut water slowly into the pot.Stir the mixture as you pour until mixture thickened. Stir the mixture constantly to prevent the batter sticks at the bottom.
Grease pan (7 x 5 inches) with little oil and pour chestnut paste into it. Steam at high fire for about 25 minutes until cake turns translucent or test it with a skewer inserted comes out clean.
Leave water chestnut cake to cool before removing it from pan.
Slice the water chestnut cake with a wet knife, serve immediately or chilled. Enjoy!