In large bowl, beat cream cheese, softened butter and 1/2 cup of the frosting with electric mixer on medium speed about 1 minute or until well blended; scrape side of bowl. Beat in egg and vanilla until smooth. On low speed, beat in cake mix until blended. Stir in 1/4 cup of the sprinkles. Drop dough by rounded tablespoonfuls 2 inches apart on ungreased or parchment lined cookie sheets.
Bake 11 to 14 minutes or until edges are light golden brown. Top with additional sprinkles while cookies are still warm. Cool on cookie sheet 2 minutes; remove to cooling rack. Cool completely, about 20 minutes.
Use leftover frosting to frost tops of cookies for an extra sweet treat. Top with additional sprinkles.
