Preheat oven to 350°F. Line cookie sheet with parchment.
In medium bowl add cupcake batter, flour, sugar, and sprinkles until just combined.
Scoop dough by 1 rounded tablespoon and place 2 inches apart onto the cookie sheet.
Bake 10-15 minutes and cool.
In medium bowl, use an electric mixer to beat the butter on medium speed until smooth and creamy.
Continue to beat while gradually adding powdered sugar.
Scrape bowl and paddle, then add vanilla.
Gradually beat in cream or milk, one tablespoon at a time, until desired consistency is reached. Continue beating until mixture is light and fluffy.
Frost cooled cookies and optionally add additional sprinkles on top.