In the same pot or skillet where the tenderloin was seared, melt butter and scrape up any fond left after searing using a wooden spoon.

Sweat (to cook slowly over low heat in butter, usually covered, without browning) shallots.

Deglaze the pan with wine, pouring in any drippings left after baking the roast.

Add vinegar and stock and bring to a boil. Turn heat down to a simmer and reduce by half.