Heat a large knob of butter in a saucepan, add a little oil to prevent it burning. Finely slice 2 red onions and fry hard for a couple of minutes. Add 1 tbsp of dark muscovado sugar along with 1 tbsp of balsamic vinegar. Stir to coat the onions and reduce the heat as low as you can. Put the lid on the pot and cook very gently for 30 minutes. The onions should be dark, sticky and melting. Season with a little salt and some freshly ground black pepper.
Serve on a good steak sandwich, along with some rocket leaves and a blob of mayo. Great for the summer.
Serves 2.
