Preheat your oven to 350°F (175°C) to ensure even baking.
In a large mixing bowl, combine the cake mix and baking powder. Stir until well mixed. Add the lightly beaten eggs, vegetable oil, and vanilla extract. Use an electric mixer on medium speed to blend until a soft dough forms.
Gently fold in the sprinkles or nonpareils using a spatula.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto ungreased cookie sheets, spacing them about 2 inches apart. Bake for 10-12 minutes, or until the edges are lightly golden.
Allow the cookies to cool on the baking sheets for about 5 minutes before transferring them to a wire rack to cool completely.
In a mixing bowl, combine the softened unsalted butter and confectioners sugar. Beat until creamy. Add the clear vanilla extract and 2 tablespoons of heavy cream or milk. Mix until smooth and fluffy.
Once the cookies are completely cooled, spread frosting on top of each cookie and sprinkle with additional sprinkles or nonpareils.
