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 10-15 minutes or until set. Remove the kuih from the cups after it is completely cooled.