Purée sweet potato in a food processor with sugar and coconut milk.
Combine the rice flour, tapioca flour and water in a mixing bowl. Add the sweet potato purée to the mix.
Spoon the sweet potato batter into lightly-greased mini cups until half-full. Steam over medium heat for about 4-5 minutes.
Top Layer: Drain the soaked sago and bring 1 cup water to a boil in a small saucepan. Add the sago and cook until transparent.
Drain and rinse under running tap water.
Combine rice flour, tapioca flour, sugar, salt and thick coconut milk in a mixing bowl. Mix into a batter, then add the sago.
Cook the mixture over low heat for about 1 minute (warm the batter but do not overcook it). Pour it onto the sweet potato layer, to fill the cups. Steam over low heat for about 1015 minutes or until set. Remove the kuih from the cups after it is completely cooled.