class RecallHistory(keras.callbacks.Callback):
    def on_train_begin(self, logs={}):
        self.recall = {}

    def on_epoch_end(self, epoch, logs={}):
        # Compute and store recall for each class here.
        self.recall[...] = 42

history = RecallHistory()
model.fit(..., callbacks=[history])

print(history.recall)