Add the fresh butter to the skillet, followed by chopped shallots. Stirring continuously with a wooden spoon, cook the shallots over medium to low heat for about 5 minutes. Take care not to let them brown.

Add the vinegar to the pan and cook 5 minutes longer, continuing to serve. Season the sauce with 3 or 4 turns of the pepper mill and add salt. Stir in the chopped parsley and any meat juices that have accumulated.