Wrap red bean paste in aluminum foil and place in the freezer until solid, at least 1 hour.

Mix glutinous rice flour and green tea powder thoroughly in a microwave-safe bowl.

Stir in water, then sugar; mix until smooth.

Cover the bowl with plastic wrap and microwave for 3 minutes 30 seconds.

Remove red bean paste from the freezer and divide into 8 equal balls.

Remove rice flour mixture from the microwave. Stir and heat, covered, for another 15 to 30 seconds.

Dust a work surface with cornstarch. Roll about 2 tablespoons of hot rice flour mixture into a ball. Flatten the ball and place one ball of frozen red bean paste in the center. Pinch and press the dough around the bean paste until completely covered.

Sprinkle with additional cornstarch and place mochi, seam-side down, in a paper muffin liner to prevent sticking.

Repeat the process to make remaining mochi.