Place ice cream, apple cider, and cinnamon in a blender and blend until smooth and creamy. Drizzle salted caramel into a glass, add milkshake, top with whipped cream if desired and drizzle with additional salted caramel.
The salted caramel recipe I use can be found here.
The amount of ice cream and cider is a general guideline, it will vary depending on your size scoop and how thick you like your milkshakes. The apple cider flavor will be stronger with less ice cream (but don't add too much or it will be too liquid-y).