Mix soy milk and sugar in a bowl.
Add glutinous rice flour and mix evenly.
Sift the dough to make it smooth.
Pour the dough into a heatproof container, cover with plastic wrap, and microwave for 2 minutes.
Remove and stir with a spatula, then microwave for another 2 minutes.
Stir once more and microwave for a final 1 minute.
Cool the dough, which will become the mochi skin, in the refrigerator.
Steam the pumpkin, mash it, then mix with soy milk and sugar to make the filling.
Dust your hands with corn starch, take a piece of dough, and spread it thinly.
Place the pumpkin filling inside and shape it into a ball.