3 tbsp white wine vinegar
3 tbsp white wine
2 shallots, finely chopped
225g/8oz/1 cup butter, chilled and diced
salt and ground black pepper
1 Put the vinegar, wine and shallots in a pan. Bring to the boil and reduce to 1 tbsp.
2 Over a low heat, whisk in the butter, a piece at a time, until the sauce thickens. Season with salt and pepper to taste.