A better than usual cover on Batman 148 (June 1962), and the story, by Moldoff and Paris, is not bad either.
The story begins as Batman and the Joker struggle in a helicopter, which crashes. Batman is knocked out, and the Joker takes the opportunity to remove his mask, which Robin sees. The Joker then publicly announces that he knows Batman’s identity, using this as a threat to keep him at bay.
Batman does not let this top him, and he pursues the Joker to a circus. The Joker takes another opportunity to try to unmask him, but Batman has set this up as a trap, to prove that the Joker really has no idea who Batman is. As can be seen in the first unmasking sequence, the light was blinding the Joker when he removed Batman’s mask, and he really saw nothing.
While this is far from a great Joker story, it’s certainly an improvement on most of what has been seen in recent years.