Blend pandan leaves and water in a food processor. Strain the mixture into a large measuring cup to extract 250ml of pandan juice. #Tip: if you need more pandan juice, put the pandan pulp back in a bowl and mix with more water then strain again.
In the measuring cup, add in the flour and sugar. Whisk till well mixed and smooth.
Add in the water chestnuts. Stir to distribute evenly. Set aside.
Prepare the baking tin
Boil the banana leaves for 10 mins, till it softens. Remove from pot, wipe dry.
Lay 1 banana leaf on the table and place the cake tin in the middle. Wrap the banana leaf around the tin and fold the leaf down in the middle. Repeat 2 more times.
Place another leaf on top of the tin and cut out out a round shape. Use a cylindrical object to push it into the baking tin and press the leaf in neatly. Repeat 2 more times.
Use a rubber band to secure the banana leaves around the tin. If not, it will curl up while it’s steaming.
Steam and serve the nian gao
Pour the batter into the tin and wrap the tin with cling foil.
Place it in the steamer and steam for 1hr 30 mins.