In a large mixing bowl, combine the sweet rice flour, sugar, and salt. Mix well to ensure there are no lumps.
Gradually add the milk and vanilla extract to the dry ingredients, stirring until the mixture is smooth and well combined.
Pour the mixture into a microwave-safe dish, spreading it evenly.
Cover the dish with a damp paper towel to prevent drying out. Microwave on high for 2 minutes.
Carefully remove the dish (it will be hot) and stir the mixture. Return it to the microwave and cook for an additional 1-2 minutes, or until the mochi is thick and slightly translucent.
Dust a clean surface with cornstarch. Pour the cooked mochi onto the surface and let it cool for about 10 minutes.
Once cooled, dust your hands with cornstarch and knead the mochi gently for a minute.
Cut the mochi into small squares or use cookie cutters for fun shapes. Dust each piece with more cornstarch to prevent sticking.