Rinse & Soak Rice: In a large bowl, combine 1 cup uncooked long-grain white rice, cinnamon stick, and 2 cups hot water. Soak for at least 4-6 hours or overnight for best flavor.
Blend Rice Mixture: Transfer soaked rice + cinnamon + soaking water to a blender. Add 3 cups cold water and blend 60-90 seconds until smooth and milky.
Strain the mixture: Pour the mixture through a fine-mesh strainer or cheesecloth into a pitcher to remove rice solids.
Sweeten & Flavor: Stir in ½ cup sugar, 1 ½ tsp vanilla extract, and 1 ½ cups milk (optional for creaminess). Taste and adjust sweetness if needed.
Chilling: Refrigerate for at least 2 hours before serving. Add ice just before serving for an extra refreshing drink.
Serve: Pour into glasses, optionally sprinkle a tiny pinch of cinnamon on top, and enjoy your authentic horchata!