In a medium-size bowl, mix mango juice and the sugar until well dissolved
Add in the rice flour ½ cup at a time until well blended.
Pour mixture into a pan and steam for 20 minutes
While waiting for the dough to steam, peel the mango and cube it for the filling.
Test for doneness when a toothpick inserted in the middle comes out clean.
Take pan out and let cool for 10 to 15 minutes
Lay cornstarch onto a wide working surface to avoid the dough from sticking to the work surface.
Also generously cover hands with cornstarch.
While still warm, scoop the dough out of the pan with a spoon covered in cornstarch and roll into medium size balls.
Flatten the dough ball and place a mango cube in the middle.
Close the ball tightly and place on a plate that is dusted with cornstarch.
Repeat until all of the dough is used.
Lightly brush the balls with water and then gently sprinkle the shredded coconut onto the balls.
(note:when rolling the balls from the dough, this part is the hardest. It is very sticky and some what difficult to work with. The cooler the dough is, the harder the dough will be to work with. Also the more cornstarch you have on your hands and use, the less it will stick to you and the dough will be easier to work with. But you can also try to line your steamer pan with a cheesecloth and then when it is ready, just lay the dough onto a cutting board that has been generously sprinkled with cornstarch and roll it into a log and then slice the dough from that instead of doing it in the procedure above. This would be easier and less messy. Also it would be better to use a ripe mango so the filling will be really nice and sweet).