Cream together the butter and the cream cheese. Add the egg and the vanilla and beat just until combined. Beat in the cake mix until well blended. Stir in ¼ cup of the sprinkles. Refrigerate at least one hour or overnight.
Preheat oven to 350 degrees. Lightly grease a cookie sheet or line with parchment paper. Scoop out rounded tablespoons of dough and roll into a 1-inch ball. Sprinkle the ball with sprinkles then roll in the confectioner’s sugar until completely covered. Place about 2 inches apart onto the prepared cookie sheet. Bake 8 to10 minutes then allow to sit on the sheet for 2 minutes before transferring to a wire rack to cool completely.