Tarragon Champagne Sauce

Heat a large saucepan over medium heat and cook capers for 30 seconds. Pour in Champagne and cook until it is reduced by half about 3 minutes. Whisk in butter 1 cube at a time until melted. Continue whisking remaining cubes of butter reserving one. Add the last cube of butter tarragon leaves lemon juice and salt. Whisk until smooth.