Prepare the Steamer: Fill a steamer with water and bring to a gentle simmer. Lightly grease an 8-inch round or square pan.
Mix Dry Ingredients: In a bowl, combine tapioca flour, rice flour, mung bean flour, sugar, and salt.
Add Coconut Milk: Gradually pour in the coconut milk, stirring constantly to avoid lumps. The batter should be smooth and slightly thick.
Divide and Color: Split the batter into two bowls. Keep one plain for the white layer. Add pandan juice to the second bowl for the green layer.
First Layer: Pour ½ cup of the white batter into the pan. Steam for 5–6 minutes until firm and glossy.
Layer Alternately: Pour ½ cup of green batter on top and steam for 5–6 minutes. Repeat alternating layers until all batter is used, finishing with a green layer.
Cool: Let the jelly cool completely for about 1 hour.
Cut and Serve: Use a lightly oiled sharp knife to cut into squares or diamonds. Serve at room temperature.