Few of us may have to worry about what to do with leftover Champagne, but should that dilemma ever be yours, you may use it here instead of white wine.

Prepare, but do not season:

using Fumet to replace the stock, if desired, if serving with fish. Have ready:

Combine in a medium saucepan and boil until reduced almost to a glaze:

Remove the wine mixture from the heat and, stirring with a wooden spoon, add the butter piece by piece so that it softens but does not liquefy and the sauce retains a creamy texture. Add:

Meanwhile, heat the velouté sauce until hot but not boiling. Whisk in the butter mixture. Season to taste with:

Serve at once.