Brew a strong cup of coffee and let it chill.
Mix flour, baking soda, cream of tartar, cinnamon, and salt in a bowl.
Beat butter and sugar until fluffy.
Add egg and vanilla, mixing until smooth.
Gradually add dry ingredients, mixing until just combined.
Roll dough into balls, then roll in cinnamon sugar.
Place on a baking sheet and bake at 350°F for 10-12 minutes.
Let cookies cool on a rack.
Pour iced coffee over ice and add milk and sugar.
Serve your iced coffee with a side of snickerdoodle cookies.