Your onion fondue is ready for use in any recipe you like.
Remarks
You will notice how the long cooking really brings out the onions' slightly sweet flavour, so do salt quite generously at the end of cooking.
It is important not to use a non-stick pan, as a conventional metal pan helps the onions to stick and create the cooking juices. These should be scraped off the bottom frequently and mixed in.
You can use clarified butter instead of the mix of oil + butter, or just normal butter, but take care not to let it burn.