Lightly coat small porcelain cups (Volume: 55 ml) with cooking oil, then arrange in steamer rack.
Add alkaline water to 100 g of water, mix well. Combine rice flour, green bean starch and tapioca starch, add in water, mix until smooth. Combine 270 g of water, brown sugar and pandan leaf in a sauce pot, bring to the boil, stir until sugar has dissolved. Add hot sugar syrup to mixture, mix until combined. Sieve mixture into stainless steel pot.
Bring ½ large pot of water to boil, turn to medium-low heat, sit stainless steel pot in hot water, cook mixture for about 1 to 1.5 minutes, until just slightly thickened.
Transfer mixture to measuring cup. Put steamer rack with small cups on steamer, pour mixture into the cups until 85% full.
Steam over medium heat for 15 minutes.
Set aside to slightly cool down for 10 minutes, then dip cups in cold water until completely cooled.
For shredded coconut: Add pinch of salt to fresh shredded coconut, mix well. Steam over medium heat for 5 minutes. Cover the steamed shredded coconut and set aside to cool.
To unmould, run a plastic knife around the edge of the cup, then take the kuih out.
Serve Dark Brown Sugar Kuih Kosui with fresh shredded coconut. (Reminder: Keep Kuih Kosui refrigerated.)