Rinse the rice through a strainer. Add to a large container with almonds, cinnamon stick, and water. Cover and let sit overnight.
Once your rice mixture has soaked for at least 8 hours, throw mixture into a blender and and blend well. Pour through a cheesecloth into a pitcher to strain out remaining chunks.
Add your rum and brown sugar. Stir to combine. Serve immediately or store in fridge until ready to use.