Sauté the shallots in a medium-sized saucepan on high until lightly browned, stirring often to stop the shallots from burning. Season with ground black pepper and add the garlic and rosemary. Continue cooking for a further 3 mins, stirring often.

Add the vinegar and cook over medium heat until the sauce has a syrupy texture. Add the wine and cook until reduced by two thirds.

Pour in the stock and bring to the sauce up to the boil. Turn down the heat and simmer until reduced by two-thirds again, to around 125ml.

Strain the sauce through a fine sieve and return to a medium-sized saucepan. Place the sauce in a warm place in the kitchen and have your butter ready to ‘monte' (whisk) this into the final sauce.