I usually just sauté onions until soft then add a splash of balsamic and call them caramelised onions. The other day I had a little more time on my hands so I followed Annabelle Langbeins recipe and think it was a winner!
6 red or brown onions, peeled and finely sliced
1 cup water
3 tbsp balsamic vinegar
2 tbsp each butter and sugar
1 tsp each salt and finely chopped rosemary leaves
(I added 1 Tbsp chopped fresh rosemary)
Combine all ingredients in a pot, cover and cook on medium heat for 15 minutes. Remove the lid and cook, stirring now and then, until all the water has evaporated and the onions are just starting to stick on the bottom (about 15 minutes). Allow to cool. Store in a jar in the fridge for up to a week.