Chop the onions into small cubes. Add butter to the pan and fry your onions with a pinch of salt for about 3 minutes. Add wine and let it cook until there is 1 tablespoon of liquid left.
Add stock and let it warm up. Add cream and bring it to boil.
Strain the sauce or blend it and put it back to the pan.
Use buerre manie to thicken the sauce. Turn the heat to medium-low and simmer the sauce for at least 10 minutes.
Season with salt, pepper and paprika powder for this beautiful colour!