Rinse the rice under cold water until the water runs clear.
Soak the rice and almonds in 4 cups of water for at least 2 hours.
Drain and rinse the rice and almonds again.
Blend the soaked rice and almonds with 2 cups of fresh water until smooth.
Strain the mixture through a fine mesh sieve or cheesecloth into a large bowl.
Add the remaining 2 cups of water to the strained mixture and stir.
Mix in the milk, sugar, cinnamon, and vanilla extract until well combined.
Chill the horchata in the refrigerator for at least 1 hour.
Serve over ice and garnish with extra cinnamon or almonds if desired.
Enjoy your homemade horchata!