Cut the Pandan leaves into small pieces. Combine the Pandan leaves and water in an electric blender. Blend for 1-2 minutes. Strain the Pandan juice through a fine sieve. Add the lye water into the Pandan juice. Set aside.
In another bowl, add the rice flour and tapioca flour. Slowly pour in the Pandan juice mixture while stirring it consistently until well blended. Add the syrup.
Cook the flour mixture on low fire until slightly thickened. Remove the mixture from heat and pour into little tea cups. Steam on high heat for 15 minutes. Take the Kuih Kosui out immediately.