In a medium saucepan, combine the wine, onions, celery, carrots and bay leaf. Bring to a boil, reduce the heat to medium-low and simmer until the liquid reduces by half, about 30 to 40 minutes. Remove from the heat and strain. Return to the pan, over medium heat. Whisk in the butter, 1 piece at a time, until the butter is incorporated, being careful not to let the sauce break. Adjust the seasoning, to taste, with salt and pepper.
Cover to keep warm until ready to serve, whisking occasionally.
Yield: about 2 cups