Blend them with 2 cups of water (500 ml). Place the mixture in a glass jar, add a cinnamon stick, and the peel of a lemon. Let the mixture stand in the fridge for at least 2 hours.
Strain the horchata using a nut milk, a cheesecloth, or a napkin and blend it with the dates and the remaining water (2 cups or 500 ml).
Let stand in the fridge until it’s cold.
You can serve the horchata with some ground cinnamon on top. Feel free to add ice too.