Preheat the oven to 350 degrees Fahrenheit. Prepare cookie sheets by lightly greasing them or lining them with nonstick baking spray.

In the bowl of an electric mixer, mix together cake mix, egg, vanilla and butter until a dough forms.

Scoop or form dough into 1 1/2" balls. Pour chocolate jimmies onto a small plate and press the dough balls into the sprinkles so the entire outside of the ball is coated.

Place cookie dough balls on prepared cookie sheets at least 2" apart. Press dough balls down with the palms of your hands to flatten.

Bake for approximately 7 to 8 minutes. Allow the cookies to cool for a few minutes on the cookie sheet before carefully removing them to a cooling rack to cool completely. Store in an air-tight container once cool.