How to make
Cut the onion into crescents and put it in a deep pan. Put olive oil on a moderate heat and stew the onions.
When the onions soften, add the sugar and stir until it caramelizes.
Then add the vinegar and stir until all of the liquid has evaporated.
Pour the wine and continue stirring until the wine has almost evaporated.
Remove it from the heat and add the butter. Stir well and allow it to cool.
Then pour the mixture into jars and store the marmalade in the refrigerator for up to 14 days.
The marmalade with onions and olive oil is ready.
