- Melt the butter (2 tbsp) in a large saucepan over low heat. Add the bacon (1), garlic or eschalots (2) and onion (1); cook until caramelised.
- Add rosemary (1), bay leaf (1), red wine (200 ml) and port (175 ml). Boil, then simmer over medium heat until reduced by half.
- Add the stock (750 ml) and reduce by half again, until thick enough to coat a spoon. Season with salt (1 tsp) to taste.
- Strain through a fine sieve. Optionally stir in a knob of butter for richness. Reheat to serve.