Mince the ginger. Combine the ginger, vinegar and 2 tablespoons of water in a saucepan. Bring to a boil and cook over high heat until liquid has almost evaporated, about 2 minutes.
Add the heavy cream and continue cooking over high heat until mixture is reduced by half, about 1 minute.
Over the lowest heat possible whisk butter into the reduction, about a tablespoon at a time, adding another piece as each is almost incorporated.
Butter should not melt completely but should soften to form a creamy sauce.
Remove from heat and season to taste with salt and pepper.