I found this on Youtube and could hardly believe my eyes/ears. This is from Korngold's mid-1930s Hollywood musical Give Us This Night starring Gladys Swarthout and Jan Kiepura, the great Polish tenor for whom Korngold created the role of The Stranger in Das Wunder der Heliane. Kiepura plays an Italian fisherman who is 'discovered' and transformed into an opera star, singing Romeo to Swarthout's Juliet. Here is the love duet that closes the opera-within-a-film and the film itself. And if you think this is OTT, just wait until you hear Heliane.
I have only ever seen this film once before, on a tiny reel-to-reel machine in the basement of UCLA in 1993. Some of the melodies are so delicious that if Pavarotti had got hold of them they'd have been world famous 20 years ago.