Heat a generous knob of butter in a large pan over low-medium heat.
Add the onions and cook until caramelised, about 10-15 minutes.
Turn up the heat and add the vinegar and coconut sugar, cook for a minute or until the sugar has melted into the onions and the vinegar has reduced; set aside and allow to cool.
Once cooled, add the onions to a bowl with the crème fraîche and chives and mix well to combine.
