Saute the shallots in a medium saucepan with the oil, over high heat for 3 minutes until lightly brown. Stir them all the time and adjust heat if they start to get too brown. Season with ground black pepper and then add the garlic and rosemary. Continue cooking for 3 more minutes. Stir all the time and adjust the heat to keep from getting too brown.

Pour in the vinegar and cook until it evaporates to a syrup, then pour in the wine and cook until reduced by 2/3.

Pour in the stock and bring to a boil. Turn down the heat and simmer until reduced by 2/3 again, to around 250 ml.

Remove the garlic and rosemary.

Add a little salt if necessary.

Finally whisk in the butter.

Serve over steak before serving.