DC Comics Bonus Book

DC Comics Bonus Books were 16-page comic book stories inserted into issues of existing DC Comics series to showcase new writers and artists. Running from April 1988 to February 1989, they consisted of a front cover, 14 pages of story, and a back cover with a brief biography of the story's creators. The addition of the insert did not entail an increase in the price of the comic book. The Bonus Books featured early work by such comics creators as Mark Askwith, Jim Balent, Randy DuBurke, Dean Haspiel, Rob Liefeld, Gordon Purcell, and Denis Rodier.

...
Wikipedia