In a mixing bowl, cover the sticky rice with plenty of water. Scrub the rice with the alum for 5 minutes, then rinse until the water runs clear. Soak the rice for another 3 hours. Drain, wrap the rice in a damp cheesecloth, and steam over medium heat for 20 minutes.

To make the coconut syrup for the sticky rice, combine coconut cream, sugar, and salt in a saucepan. Cook over low heat, stirring until the sugar and salt dissolve. When it just starts to boil, remove from heat. Divide the syrup into two portions. Add pandan juice to one and butterfly pea flower juice to the other, stirring each to combine.

Divide the hot, freshly steamed sticky rice into two portions. Add each portion to one of the coconut syrup mixtures and stir to combine. Cover and let sit for 15 minutes. Then uncover, stir the rice, and cover again for another 15 minutes. For the coconut sauce topping, mix coconut cream, water, salt, and rice flour in a saucepan. Stir until the flour dissolves. Cook over low heat, stirring until the sauce thickens slightly.

Soak the shelled mung beans in cold water for 30 minutes. Drain and let dry, then toast over low heat until golden and crispy. The sticky rice is now ready.

Peel the ripe mango and slice thinly across the grain. Press the sticky rice into a mold, layering with mango slices. Start with the larger mango pieces around the edge and work toward the center.

Top with coconut sauce and sprinkle with toasted mung beans. Serve and enjoy!