Preheat oven to 350 °F . Line cookie sheet with parchment paper or other cookie pan liner. Set aside and prepare cookie dough.
In large mixing bowl, cream the butter, sugar, and powdered sugar together until smooth and creamy. Add in eggs, cake batter and vanilla extracts and continue mixing until well combined.
Next, add in flour, baking powder, and salt. Mix just until all ingredients are well combined and flour is no longer visible. Do not overmix. Stir in sprinkles by hand.
Use a large cookie scoop to evenly scoop 6 cookie dough balls onto each baking sheet. Next, gently flatten scooped dough until about 1 inch thick. Bake cookies in oven for 12 minutes. Allow to cool on baking sheet for 5-10 minutes, then transfer to cooling rack.
Meanwhile while cookies are cooling, prepare the frosting.
Birthday Cake Cookie Frosting
Cream together cream cheese and butter until smooth and creamy. Add in cake batter extract and powdered sugar. Continue mixing until all ingredients are well combined and frosting is light and fluffy.
Place frosting in piping bag with large round tip, or use a Ziploc bag with end cut off. Pipe frosting on cooled cookies and sprinkle with additional sprinkles. Serve cookies and enjoy!