Rinse the rice under cold water until the water runs clear.

Place the rice in a large bowl and cover with water. Let it soak for 24 hours.

Drain the rice and place it in a blender or food processor. Add water and blend until smooth.

Transfer the blended rice mixture to a large pot and bring to a simmer.

Reduce the heat to low and cook for 30 minutes, stirring occasionally.

Remove from heat and let the mixture cool to about 140°F (60°C).

Add koji, honey or sugar, salt, and vanilla extract (if using) to the pot and stir until well combined.

Cover the pot with a clean kitchen towel and let it sit at room temperature for 8-12 hours to ferment.

After fermentation, refrigerate the amazake and serve chilled.