- 2 onions, halved and sliced
- A large knob of butter
- 500ml beef stock
- 1 tbsp wholegrain mustard
- Place the onions, butter and a pinch of salt in a medium pan cook over a low heat for about 30 minutes, stirring, until dark brown and caramelised.
- Add the stock and mustard, simmer for 20 minutes.
Tip: Red or white onions both work for this recipe.