Let's cook.
In a microwave-safe bowl, combine the glutinous rice flour, granulated sugar, and matcha powder. Whisk well to ensure there are no lumps.
Gradually add the water to the dry ingredients, stirring continuously until a smooth, lump-free batter forms.
Cover the bowl loosely with plastic wrap, leaving a small vent. Microwave on high for 2 minutes.
Carefully remove the bowl and stir the mixture with a wet spatula. Re-cover and microwave for another 1 to 2 minutes, or until the mochi is translucent and sticky.
While the mochi is still warm, dust a clean work surface generously with cornstarch. Transfer the cooked mochi onto the cornstarch.
Dust your hands and a rolling pin with cornstarch. Gently flatten the mochi into a rectangle about 1/4-inch thick.
Using a sharp, cornstarch-dusted knife or a pizza cutter, cut the mochi into 8 equal squares or rectangles.
Dust each piece with additional matcha powder for extra flavor and color, if desired. Serve immediately or store.
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