The Joker decides to spread out across the 48 states that make up the US at this time, in Batman 55 (Oct/Nov 49).
The Joker sets up a school to train his franchised Jokers in this Finger, Sprang and Kaye story. Very little of the tale actually deals with the 48 Jokers, most of it takes place at the training school.
Batman gets a post as one of the Joker trainees, but stupidly wears his mask under the joker outift, which reveals his identity.
The Joker then makes Batman dress up in a clownish version of his costume, and spends his time humiliating him. Robin gets captured, but breaks free and helps Batman take down the original Joker. They then send out a message to the other Jokers, bringing them together and rounding them up.