Combine ice cream, 1/2 cup milk, cinnamon, and 3 of the snickerdoodles, broken into smaller pieces, in your blender. Blend until cookies are incorporated. Add up to 1/2 cup more milk and blend until milkshake reaches your desired consistency.
Take a heaping spoonful of caramel and drizzle it around the inside of your 16-ounce glasses. Divide milkshake evenly between them.
Things get messy from here, so if you are going to line the rims of your cups with caramel, make sure the cups are on a plate to catch the drips and are where you plan on drinking them! Use a spoon to drizzle caramel around the edges, letting some of it fall into the cup as well.
Top with whipped cream.
Crumble the remaining cookie and sprinkle over the top.
Add a cute straw, drink responsibly, and enjoy!
In the ingredients, I linked to my favorite snickerdoodle cookie recipe, but those cookies are half-sized, so double the number of cookies in the shake. Or save yourself some time and buy them. It's up to you!