Mix glutinous rice flour, sugar, and water in a pot, making sure there are no lumps.
Warm the mixture over low heat. When it starts to thicken, cook it for 5 minutes, stirring it vigorously, until you have a smooth and stretchy dough.
Transfer the mochi dough onto a worktop dusted with corn starch. Then, dust the dough with some starch to make it less sticky.
Pinch off a small handful of dough and shape it into a ball.
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{{/ items}} {{^ items}} {{/ items}}Flatten one ball into a thick 7cm (2.5 inches) disc. Then, brush off excess starch on both sides.
Then, scoop a spoonful of cold ube butter, roll it into a ball, and place it in the centre of the disc.
Pull the edges of the dough towards the centre and over the filling, pinching them together at the top.
Then, hold the mochi in your hand and keep pinching the dough together while you twist the mochi to make a tight ball.
Flip the mochi seam-side down and lightly press it into a dome shape. Enjoy!