Bring a medium pot of water to a boil over high heat. Cut a small cross in the bottom of each peach, boil for 1 minute, then transfer to cold water, peel, and halve.

In a microwave-safe bowl, mix glutinous rice flour and sugar. Gradually whisk in water until smooth. Cover with a wet paper towel and microwave on high for 1 minute, stir, and repeat for a total of three times.

Dust your work surface generously with cornstarch while the dough cools.

Flatten the cooled mochi dough into a circle about ⅙-inch thick.

Divide the dough into four portions, place a peach half in the center of each, and carefully enclose it.

Pinch the dough together at the top to seal. Dust with cornstarch and place seam-side down.

Repeat the filling process with remaining peach halves and dough.

Serve immediately or refrigerate in an airtight container.