Continue to boil for 2 minutes, stirring constantly.
Add the milk and the cinnamon and bring to a boil, still stirring constantly.
Cool to lukewarm.
Gradually add the powdered sugar and beat until thick enough to spread.
Video
Notes
I used Eden apple butter, which is oh-so-tasty! However, if you would like to make your own apple butter, check out these sites for apple butter recipes: