Oat milk, vanilla
In a blender, combine the white rice and water. Blend until the rice is finely ground. Add the cinnamon stick and blend for an additional 30 seconds.
Pour the rice blend into a large bowl, cover, and let it soak at room temperature for 4 to 6 hours, or overnight.
After soaking, strain the mixture through a fine mesh sieve or cheesecloth into a pitcher. Press down to extract as much liquid as possible. Discard the solids.
Stir in the oat milk, vanilla extract, and sugar into the strained mixture until well combined.
In a small bowl, whisk the matcha powder with 2 tablespoons of hot water until smooth and no lumps remain.
In a glass, pour in the horchata base and add the whisked matcha on top. Stir gently to combine and serve over ice.