How to Make It
Combine first 4 ingredients in a saucepan; bring to a boil over medium-high heat. Reduce heat, and simmer until reduced to 1 cup. Strain mixture through sieve into a bowl, discarding solids.
Return wine mixture to saucepan; cook until mixture is reduced to 1/2 cup. Reduce heat to low; add unsalted butter, 1 piece at a time, stirring with a whisk. (Do not overheat or sauce will separate.) Add salt.