This is a recipe my Dad emailed me a few years ago which I found again recently while I was sorting out some old emails. It takes a bit of work to make but it's worth it:

The recipe makes 300 g of the marmalade
1 kg peeled red onions
100ml olive oil
1 tsp sea salt
1/2tsp black pepper
2 bay leaves
2 sprigs rosemary
150g caster or soft brown sugar - we used the latter
100ml dry white wine
75ml red wine vinegar

Cut onions in half and slice finely and cook in the oil for approx 5 mins or until soft.
Add salt,pepper,bay and rosemary ,cover and cook over gentle heat for approx 20 mins until wilted and soft stirring occasionally Add sugar,wine and vinegar and bring to the boil,stirring.Reduce the heat and cook uncovered for 20/30 minsuntil soft and sticky and most of liquid absorbed.need to stir fairly constantly at the end to avoid sticking.Pick out the bay and the rosemary and discard.Spoon into 2 150ml jars and leave to cool,then seal tightly.Jars should be sterilised.your mum put them in microwave 3/4 full of water and allow to boil for a while. Empty and leave to dry. Your mum dries them in a low oven on gentle heat.
Ideally the marmalade should be left for a week before use for best results but not essential. Once open can store in fridge for 3 weeks.

My Dad's email continued to say that it works really well with cheese on toast.