In a large bowl, combine rice, almonds and cinnamon sticks. Cover with warm water and let soak for 5hours, or overnight, until rice and cinnamon sticks have softened.
Strain and discard water from rice mixture. Pour mixture into a blender. Add evaporated milk, cover and blend on high. The mixture should be thick and smooth.
Push mixture through a fine-mesh sieve, into a pitcher. Stir in water, whole milk, sugar, and vanilla. Stir to combine thoroughly. Refrigerate to chill, at least 30 minutes.
To serve:
Divide horchata among ice-filled glasses and top with cold brew concentrate, to taste (about 2 to 3 tablespoons cold brew for each cup of horchata).
Enjoy!
Notes
The horchata is best consumed the day it's made, but will keep up to 2 days in a covered container in the refrigerator. Stir vigorously before serving.