A fun and delicious layer cake made out of cookies!
With mixer off, add the powdered sugar and cocoa mixture. Turn mixer on to low and then slowly combine.
Add in milk. Turn mixer to medium high and mix until combined. You will want to pour the frosting over cookies so make sure it is the right consistency. If you need to add more milk then do so.
Beat butter and vanilla in bowl of stand mixer with whisk attachment on medium-high speed until light and fluffy.
With mixer on low, slowly add in confectioners' sugar , milk, and salt; frequently scrape sides and bottom of bowl.
If frosting is too thick to spread, gradually beat in additional milk. You want the frosting to be pourable.