Using an ice cube tray, freeze 2 cups of apple cider until hardened, around 4 hours.
To a blender, add in apple cider ice cubes, bourbon, and orange juice. Blend until thoroughly combined and a smooth slush has formed. Add in desired amount of ginger beer, and pulse for a few additional seconds to incorporate.
Divide mixture into two copper moscow mule mugs. Garnish with apple slices dipped in cinnamon sugar.
If making ahead of time, place the copper mugs filled with the slushie into the freezer to keep frozen. Once you're ready to serve, remove the mugs for a few minutes, and add garnish.For a mocktail version, omit the bourbon.