Onion sauce is a standard French kitchen classic which is excellent with roast beef, steaks, liver or bratwurst.
- Put the onions into a pan with the water and cook very slowly over a low heat for 50-60 minutes. The sugar in the onions will slowly caramelise and become brown and sweet.
- Add the stock and simmer for a further 15-20 minutes.
- Serve in a warm dish.