Heat a heavy saucepan over medium heat and add the butter.
Saute the celery, onion and carrot until caramelized, should take about 5-6 minutes.
Now add tomato paste and continue to cook one more minute.
Yous should now add the flour, tossing to coat the vegetables, and cook for one minute more. Deglaze the pan with the wine, scraping any fond off the bottom of the pan.
Add the bay leaf and stock and whisk to combine the ingredients. Bring the sauce to a boil, reduce the heat to a simmer and cook, uncovered, for about 10-15 minutes, or until the sauce is reduced slightly and vegetables are soft.
Pass through a food mill or strainer into another pot and mount with the cold butter.
Video
Notes
Try adding 1 tablespoon of Dijon mustard to the finished sauce.