Combine ½ cup (125 milliliters) of white wine vinegar with ½ cup (125 milliliters) of white wine and reduce the mixture by half. Add 3 cups (750 milliliters) of sauce velouté to the reduction and bring the mixture to a simmer. Remove the sauce from the heat and finish it with 3 ounces (75 grams) of shallot butter. This sauce will probably need to be thinned with stock, heavy cream, or milk.