Pour 3 cups of the apple cider into an ice tray and freeze until solid, 4 to 6 hours. Once frozen, transfer the cubes to a blender with the remaining ingredients and blend into a smooth slushie consistency. Divide between glasses and serve.
Pro tip: If you, like the rest of us, don’t have a slushie machine at home, freeze the cider into ice cubes before blending. It’s a trick Fields thinks “is absolutely brilliant.”